=head1 NAME

Rosetta::Framework - Documentation on the Rosetta framework at large

=head1 ABSTRACT

Rosetta is a comprehensive framework for database-using applications of any
size or function that allows them to be easily portable across multiple
database implementations because any proprietary details of each are abstracted
away.  At the same time, it is designed to be fast and efficient.  Applications
use Rosetta as a virtual embedded database, whose API is called the "Rosetta
Native Interface" or "RNI", and whose feature set is an opaque normalized
superset of all common database feature sets.  The feature superset includes
both data manipulation (with multi-table selects and updates plus subqueries or
stored procedure calls) and schema manipulation (tables, views, procedures).
Rosetta is designed to work equally well with both embedded and client-server
databases; in the latter case, it is the client.

The RNI is implemented using mainly a "Command" design pattern, meaning that it
has few real functions or methods, but those use objects as input and output,
which are flexible enough to define any task or result.  The RNI is verbose and
intended to provide non-ambiguous structured definitions of all tasks, so that
the results of executing them are easy to predict; the definitions are
multi-dimensional data structures (or objects) having atomic values (which also
have native data type formats).  Rosetta has this as an advantage over other
database abstractions that use serialized strings like SQL (such as ODBC/JDBC),
because each database has its own SQL dialect, and applications using them must
be coded differently for each one.  Rosetta is especially suited for
data-driven applications, since the composite scalar values in their data
dictionaries can often be copied directly to RNI structures, saving
applications the tedious work of generating SQL themselves.  Rosetta also
provides native internationalization support, for example allowing system
messages to be in multiple user languages simultaneously.

Rosetta makes it easy to layer alternative APIs on top of RNI, so that you can
simplify or customize it to your specific needs.  As practical examples of
this, there are several emulators provided for common existing database APIs
(such as ODBC/JDBC), so that most applications can simply use Rosetta as a
hot-swappable replacement for them; you do not have to "learn yet another
language" or re-code your application in order for it to just work with more
databases.  While the Rosetta core must always be embedded in an application to
be used, an extension is available that will allow it to be used in a
client-server arrangement instead (as ODBC does), where the server is a proxy
for the client; the client is embedded in the main application, and it talks to
the server in network-serialized RNI, which then translates the request into
native database actions.  Some utilities built on Rosetta are also available,
for such tasks as cloning or backing up a database (schema and/or data; this
includes scanning the database to make a data dictionary), or editing one
through a web interface (like PHPPgAdmin or PHPMyAdmin but for any RDBMS).

Rosetta is not a complete database by itself and you need to separately have an
actual database to use it with.  Rosetta does not usually implement features
that are missing in a database being abstracted (such as foreign key
constraints, transactional integrity, or geographical data types), in order to
give it an identical feature set to a more capable database; Rosetta just
allows for the features that do exist to be called in an identical way.  A
consequence of this is that your choice of database implementation will indeed
affect what features you have available; your application will port without
changes only to databases which support the features that you use.  The RNI may
not interface to every single feature of a particular database (neglecting
esoteric ones), so you can't use those features with Rosetta (but support can
be added).  Rosetta does not automate installation of any separate database
software or configure it (like a package manager); you will have to do that
yourself.

Note: see also the SQL::SyntaxModel library, which is the foundation for the
Rosetta API; see the Language.pod file in particular.

=head1 COPYRIGHT AND LICENSE

This file is part of the Rosetta database portability library.

Rosetta is Copyright (c) 1999-2004, Darren R. Duncan.  All rights reserved.
Address comments, suggestions, and bug reports to B<perl@DarrenDuncan.net>, or
visit "http://www.DarrenDuncan.net" for more information.

Rosetta is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License (GPL) version 2 as published by the
Free Software Foundation (http://www.fsf.org/).  You should have received a
copy of the GPL as part of the Rosetta distribution, in the file named
"LICENSE"; if not, write to the Free Software Foundation, Inc., 59 Temple
Place, Suite 330, Boston, MA 02111-1307 USA.

Linking Rosetta statically or dynamically with other modules is making a
combined work based on Rosetta.  Thus, the terms and conditions of the GPL
cover the whole combination.  As a special exception, the copyright holders of
Rosetta give you permission to link Rosetta with independent modules,
regardless of the license terms of these independent modules, and to copy and
distribute the resulting combined work under terms of your choice, provided
that every copy of the combined work is accompanied by a complete copy of the
source code of Rosetta (the version of Rosetta used to produce the combined
work), being distributed under the terms of the GPL plus this exception.  An
independent module is a module which is not derived from or based on Rosetta,
and which is fully useable when not linked to Rosetta in any form.

Any versions of Rosetta that you modify and distribute must carry prominent
notices stating that you changed the files and the date of any changes, in
addition to preserving this original copyright notice and other credits.
Rosetta is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

While it is by no means required, the copyright holders of Rosetta would
appreciate being informed any time you create a modified version of Rosetta
that you are willing to distribute, because that is a practical way of
suggesting improvements to the standard version.

=head1 SYNOPSIS

I<None present at the moment.  Meanwhile, see the EXAMPLE PROGRAM below.>

=head1 DESCRIPTION

The Rosetta framework is intended to support complex (or simple) database-using
applications that are easily portable across databases because common
product-specific details are abstracted away.  These include the RDBMS product
and vendor name, what dialect of SQL its scripting or query interface uses,
whether the product uses SQL at all or some other method of querying, how query
results are returned, what features the RDBMS supports, how to manage
connections, how to manage schema, how to manage stored procedures, and perhaps
how to manage users.  The main thing that this framework will not be doing in
the forseeable future is managing the installation and configuration of the
RDBMS itself, which may be on the same machine or a different one.

There are two main types of functionality that the Rosetta framework is
designed to implement; this functionality may be better described in different
groupings.

The first functionality type is the management (creation, modification,
deletion) of the schema in a database, including: tables, keys, constraints,
relations, sequences, views, stored procedures, triggers, and users.  This type
of functionality typically is used infrequently and sets things up for the main
functionality of your database-using application(s). In some cases, typically
with single-user desktop applications, the application may install its own
schema, and/or create new database files, when it starts up or upon the user's
prompting; this can be analogous to the result of a "New..." (or "Save As...")
command in a desktop financial management or file archiving application; the
application would then carry on to use the schema as its personal working
space.  In other cases, typically with multiple-user client-server
applications, one "Installer" or "Manager" type application or process with
exclusive access will be run once to create the schema, and then a separate
application or process will be run to make use of it as a shared working space.

The second functionality type is the management (creation, modification,
deletion) of the data in a database, including such operations as: direct
selects from single or multiple tables or views, direct inserts or updates or
deletes of records, calling stored procedures, using sequences, managing
temporary tables, managing transactions, managing data integrity.  This type of
functionality typically is used frequently and comprises the main functionality
of your database-using application(s).  In some cases, typically with
public-accessible websites or services, all or most users will just be viewing
data and not changing anything; everyone would use the same database user and
they would not be prompted for passwords or other security credentials.  In
other cases, typically with private or restricted-access websites or services,
all or most users will also be changing data; everyone would have their own
real or application-simulated database user, whom they log in as with a
password or other credentials; as the application implements, these users can
have different activity privileges, and their actions can be audited.

The Rosetta framework can be considered a low-level service because it allows a
fine level of granularity or detail for the commands you can make of it and the
results you get back; you get a detailed level of control.  But it is not
low-level in the way that you would be entering any raw SQL, or even small
fragments of raw SQL; that is expressly avoided because it would expose
implementation details that aren't true on all databases.  Rather, this
framework provides the means for you to specify in an RDBMS-generic fashion
exactly what it is you want to happen, and your request is mapped to native or
emulated functionality for the actual RDBMS that is being used, to do the work.
The implementation or mapping is different for each RDBMS being abstracted
away, and makes maximum use of that database's built-in functionality. Thereby,
the Rosetta framework achieves the greatest performance possible while still
being 100% RDBMS-generic.

This differs from other database abstraction modules or frameworks that I am
aware of on CPAN, since the others tend to either work towards the
lowest-common-denominator database while emulating more complex functionality,
which is very slow, or more often they provide a much more limited number of
abstracted functions and expect you to do things manually (which is specific to
single databases or non-portable) with any other functionality you need.  With
many modules, even the abstracted functions tend to accept sql fragments as
part of their input, which in the broadest sense makes those non-portable as
well.  With my framework I am attempting the "holy grail" of maximum
portability with maximum features and maximum speed, which to my knowledge none
of the existing solutions on CPAN are doing, or would be able to do short of a
full rewrite.  This is largely why I am starting a new module framework rather
than trying to help patch an existing solution; I believe a rewrite is needed.

The Rosetta framework is best used through its native interface (RNI), which
accepts and returns only atomic values (or multi-dimensional data structures
containing them); no "parsing" or such analysis is done such as with SQL
statements.  The main reason is that this framework is intended primarily for a
data-driven application programming model, where the applications use a "data
dictionary" to control what work it is doing; the applications can simply copy
the composite scalar values of the data dictionary, without having to encode
them into a single string.  The RNI is designed to allow entry of a
non-ambiguous structured definition of any task that you would want a database
to do.  Rosetta is intended to support a superset of features from all common
generic RDBMS products, so it should have a native way of expressing any task
that you can do now.  For cases where you don't already have a data dictionary,
Rosetta can scan your existing database to create one.

One would think that, despite all the advantages that Rosetta can bring to a
new application that is designed around RNI (or a simplifying wrapper of it),
it wouldn't be very helpful to an existing older application that is built
around "a different way of doing things".  From the latter perspective, there
looks to be just as much work involved in porting their application to use
Rosetta as there would be to port it to a new database or other interface
framework.  The problem would be the all-too-common having to "learn yet
another language", and then port the application to it (for that matter, it
would be a new language for new app builders as well, although that may not be
the same problem).  Either transition could be a significant cost and the
hurdle can deter upgrades to making apps portable.

But to help with this situation, Rosetta also includes several emulators (each
of which is a higher-level layer that translates its input into RNI calls) for
common existing database interfaces, so that most applications can simply use
Rosetta as a hot-swappable replacement for them; you do not have to "learn yet
another language" or re-code your application in order for it to just work with
more databases.  It should be possible to emulate any existing interface, and
if a new one comes along with features that Rosetta can't handle (interface to
or implement), then this is a reasonable excuse to update the core so that it
is possible.  That said, the success of an emulator depends largely on whether
code that was using the original module is using the original the way it was
designed or not; code that was hacking the internals of a module (as Perl makes
so easy) is less likely to work (sort of like how an app used to using
un-documented APIs on an operating sytem, or doing direct OS data structure
access on a non-memory-protected OS, would break if the implementation of that
OS changed).

Included in a Rosetta distribution will be several applications which serve
as examples of Rosetta in use, but in some cases are useful themselves.  One
example will be a utility for copying one database to another, such as for
backup or restore, or just migration.  Another example will be a web app that
works sort of like "PHPPgAdmin" or "PHPMyAdmin" (letting users manually edit
schema and data) except that it works with many RDBMS products.  Some code
porting utilities could also be available, to help makers of old applications
migrate to RNI, for better control and performance than an emulator would
provide.

=head1 STRUCTURE

The modules composing the Rosetta framework are grouped into several main
categories, which can be called: "Locale" (Locale::KeyedText), "Model"
(SQL::SyntaxModel), "Interface", "Engine", "Proxy" (Server/Client), "Validator",
"Emulator", and others.

Note: the file Language.pod should be read next, after Framework.pod.

These classes do not export any functions or methods, so you need to call them
using object notation.  This means using B<Class-E<gt>function()> for functions
and B<$object-E<gt>method()> for methods.  If you are inheriting any class for
your own modules, then that often means something like B<$self-E<gt>method()>. 

This briefly illustrates the relationship of the module groups:

	           DATABASE
	              |
	              |
	     Proxy    |
	     Client;Engine--------------\
	    called by |   uses   used by \
	              |                   \
	      invokes |                    \
	          Interface--------------Model;Locale (both used by other 7 groups)
	    called by | \ uses   used by /  |
	              |  \              /   |
	      invokes/|   \            /   /
	            //| Emulator------/   /
	Validator--// | | uses   used by /
	           /  | |               /
	     Proxy/   | |              /
	     Server APPLICATION-------/
	                  uses   used by

The Locale modules function as constant data resources, mainly holding
user-readable text such as database error messages and so forth, so that this
text is separate from normal module code and easy to edit.  These are part of
the Rosetta core, and are used by the Interface and Engine modules.  There are
multiple Locale files rather than just one partly so that each file can have a
different localization; adding a new user language is as easy as adding another
file.  The set of text strings being stored should be comprehensive enough that
any Engine module can use them, and therefore not need their own Locale files
for displaying error messages.  All strings are mapped to short codes (eg:
'R001372'); these codes are what the normal module code uses to display a
particular message.

The "Model" and "Interface" modules are collectively referred to as the "Rosetta
Native Interface" or "RNI", and they are the "Core" of the Rosetta framework to
which all else is attached.  The distinction between the two is that Model
modules are purely container objects which hold descriptions of "things" (such
as data types or tables or views), while Interface modules typically are not
containers and represent "actions" (such as connections or cursors).  Model
objects are complete on their own and can be serialized or stored indefinately
off site for later retrieval and use, such as with a "data dictionary"
describing a table or view.  Interface objects only make sense within the context
where they were created and often contain time-sensitive data; it wouldn't make
sense to store them except during the short term, such as with a pool of active
and reusable database connections.  It is common for Interface objects to hold
Model objects as properties, to help them know how to do their actions, such
as how to create a table or select from it.

The Engine modules are what enable Rosetta to use each type of database.  They
are what handle (interface to or implement) all the details of using a specific
RDBMS product; you need at least one for each unique RDBMS product you plan to
run your application on; they are "action" modules.  They take Interface/Model
objects as input and convert them into the actual SQL or other method calls
that the RDBMS products use, then they invoke the generated, and then interpret
the results into other Interface/Model objects to return as output.  The Engine
modules also deal with extracting any existing schema stored in an RDBMS so
they can generate an RNI data dictionary from it when desired.  Nothing talks
to an RDBMS product except a Engine module, and nothing talks to an Engine
module except the Interface modules.

Note that application specific "stored procedures" which are implemented in
Perl, and that are RDBMS product specific, would sit beside "Engine" in the
above diagram, since they would have direct access to the product-specific code
that the Engine uses to talk to the DATABASE.  Those are not shown in the above
diagram for simplicity.  That said, all calls to such "stored procedures" from
the main APPLICATION will still always go through Interface.

The Proxy modules comprise an extension that allows the normally embedded-only
Rosetta to be used in a client-server situation (as ODBC is).  But this
extension is implemented in such a way that neither the Engine modules nor the
APPLICATION need to know the difference of whether the extension is being used
or not.  The Proxy modules correspond to both a "Engine" (network client) and
an "APPLICATION" (network server); they involve two applications that have the
Rosetta core embedded talking to each other, with one handing all the database
details on behalf of the other.  See the following diagram:

	  DATABASE
	     |
	   Engine
	     |
	 Interface::::::
	     |         =
	Proxy Server   =
	     |         =
	  NETWORK      = (Engine and APP think these are the same single Interface)
	     |         =
	Proxy Client   =
	     |         =
	 Interface::::::
	     |
	APPLICATION

The Validator modules are a common comprehensive test suite to run against all
Engines in order to tell that they are implementing the Rosetta interface
properly or not.  This also saves each Engine maker from having to write their
own tests.  These would be used similarly to how Sun has an official validation
suite for Java Virtual Machines to make sure they implement the official Java
specification.  Since not all databases are alike, each Engine is expected to
report programmatically which kinds of features it supports, and the validator
suite will only test interface compliance for those features; this way, a
missing feature does not mean the Engine will fail its tests unless it
explicitly says it has said feature.

The Emulator modules are extensions that are purely optional for use, and they
are intended to facilitate rapid adaption (hot-swapping) of Rosetta into an
existing application that is already built around a different database
interface (such as DBI or ODBC or OCI).  Each Emulator module is a higher-level
layer which translates its input into pure RNI calls and translates the output
correspondingly; each should have an identical public interface to what it
emulates.  So applications often won't need to be changed to use Rosetta, but
they still just become more portable.  Many Emulator modules would include SQL
parsing functionality (as SQL is their input), and would convert SQL statements
from known dialects into Interface/Model objects

All of the Rosetta components are implemented using pure Perl 5 code for now
and during the near future (although some Engines or extensions may have
prerequisites that are not).  Once Rosetta is feature complete in this form, it
will be rewritten as a C library which has bindings for multiple languages,
including Perl 5 and Parrot.  Advantages of this change are not only greater
speed and memory efficiency but also compatability; it will allow Rosetta (and
through it Perl) to use databases which previously had no Perl bindings or DBI
Engines before.  Moreover, the potential user base would increase sharply
because users of other languages like PHP or Python would be able to use it.
The C version of Rosetta will probably have the "Model" (SQL::SyntaxModel) and
"Interface" modules being mostly reduced to struct definitions, macros for
manipulating the structs, header files, and a small amount of implementation
code.  Most of the normal implementation C code would be derived from the other
modules, particularly the "Engine", "Proxy", "Validator", "Emulator" ones.  The
pure Perl version will probably stay around after that conversion should it be
useful, but it won't have as large of a database support.  I have no plans to
make a pure Java version, but rather, the C version would bind to Java
environments using a Java Bean.

=head1 AN ALTERNATIVE SECOND VERSION

Inspired by the recent (February 2004) formation of dbdi-dev@perl.org, a group
which aims to make a Parrot-native database access framework for all Parrot
hosted languages, and that can talk to native database drivers through Parrot's
Native Call Interface, meaning that the Parrot database project doesn't need
any parts written in C, I may decide to take the same approach with the next
major version of Rosetta and related projects, implementing it in IMC
instead of C.

=head1 BRIEF MODULE LIST

The following module names and descriptions are undergoing a state of
transition, mainly in the 'Extensions' arena.  See below for details.  Many of
these modules don't exist yet, but are being planned to exist, as they are
implemented over time.

I<Any indented package names represent inner classes of what they are beneath.>

=head2 In distribution "Locale-KeyedText"

	Locale::KeyedText (Refer to user messages in programs by keys)
		Locale::KeyedText::Message (stores details of a machine-readable message)
		Locale::KeyedText::Translator (converts a m-r message to a human readable form)

=head2 In distribution "SQL-SyntaxModel"

	SQL::SyntaxModel (An abstract syntax tree for all types of SQL)
		SQL::SyntaxModel::Container (a context for Nodes, one of these per parent)
		SQL::SyntaxModel::Node (a semi-atomic model component)
	SQL::SyntaxModel::L::en (Localization of SQL::SyntaxModel for English)
	SQL::SyntaxModel::L::fr (Localization of SQL::SyntaxModel for French)
	SQL::SyntaxModel::L::* ... like German, Spanish, Dutch, Chinese, etc

	SQL::SyntaxModel::Language (What language or grammar SQL::SyntaxModel speaks)
	SQL::SyntaxModel::API_C (Describe the core C API for SQL::SyntaxModel)

=head2 In distribution "Rosetta"

	Rosetta (Framework for RDBMS-generic apps and schemas)
		Rosetta::Interface (defines the whole Rosetta public API, is largely a shim)
		Rosetta::Engine (common base class for Engine modules that implement the Rosetta API)
		Rosetta::Dispatcher (handle requests not directed at any particular Engine)
	Rosetta::L::en (Localization of Rosetta core for English)
		(Also provides a set of generic database error strings for Engines, in English)
	Rosetta::L::fr (Localization of Rosetta core for French)
	Rosetta::L::* ... like German, Spanish, Dutch, Chinese, etc

	Rosetta::Features (What RNI features a Rosetta Engine can possibly implement)
	Rosetta::Framework (Documentation on the Rosetta framework at large)

	Rosetta::Validator (A common comprehensive test suite to run against all Engines)
	Rosetta::Validator::L::en (Localization of Rosetta::Validator for English)
	Rosetta::Validator::L::fr (Localization of Rosetta::Validator for French)
	Rosetta::Validator::L::* ... like German, Spanish, Dutch, Chinese, etc

=head2 In temporary distribution "Rosetta-Extensions"

During the short term, these following modules will have their first
versions, both v0.01 and several later, released all as part of a single
distribution, Extensions.  The idea here is to keep down the number of
distributions that are always being released in tandem, because each saw major
changes in each update round.  Once these are modestly stable I will probably
split them up such as is seen in the other module blocks, below.

	Rosetta::Extensions (Reference implementations of fundamental Rosetta features)
		(File is a small place-holder POD file to represent the distribution on CPAN)
	Rosetta::Engine::Generic (A catch-all Engine for any DBI-supported SQL database)
	Rosetta::Engine::Generic::L::en (Localization of Rosetta::Engine::Generic for English)
	Rosetta::Utility::SQLBuilder (Generate ANSI/ISO SQL-2003 and other SQL variants)
	Rosetta::Utility::SQLParser (Parse ANSI/ISO SQL-2003 and other SQL variants)
	Rosetta::Emulator::DBI (emulates DBI/DBD::*, but result is more portable)

=head2 In distribution "Rosetta-Utilities" or a multiplicity of similarly named

	Rosetta::Utility::SQLBuilder (Generate ANSI/ISO SQL-2003 and other SQL variants)
	Rosetta::Utility::SQLParser (Parse ANSI/ISO SQL-2003 and other SQL variants)
	Rosetta::Utility::RWViews (convert IUD against views into IUD against tables)
	Rosetta::Utility::* ... other non-core utility modules usable by several non-core distros

=head2 In distribution "Rosetta-Engine-Generic"

	Rosetta::Engine::Generic (A catch-all Engine for any DBI-supported SQL database)
	Rosetta::Engine::Generic::L::en (Localization of Rosetta::Engine::Generic for English)

=head2 In a multiplicity of "Rosetta-Engine-*" distributions

These Engine names are examples which I probably won't implement myself any
time soon, if at all.  I leave these open for anyone who wants to make an
Engine for one or more databases, either that does a more "proper" job than my
own Generic catch-all, or to support a database or service my catch-all doesn't
support at all, such as a non-SQL based one, or who for example want to use 
something not DBI based like Win32::ODBC.

I<Note: more databases (and data access protocols) can be found listed at 
"http://freshmeat.net/articles/view/305/" and "http://freshmeat.net/articles/view/307/">

	Rosetta::Engine::SQLite (binding to public domain SQLite embedded db; default RDBMS for Rosetta)
	Rosetta::Engine::Oracle (interface to Oracle db 8, 9)
	Rosetta::Engine::Sybase (interface to Sybase db)
	Rosetta::Engine::PostgreSQL (interface to PostgreSQL db 8.0.x, 7.4.x, 7.3.x)
	Rosetta::Engine::MySQL (interface/binding to MySQL cli-serv/embed db 4.x, 5.x, 3.23.x)
	Rosetta::Engine::Informix (interface to IBM Informix db)
	Rosetta::Engine::DB2 (interface to IBM's DB/2 db and its DB/2 Express db)
	Rosetta::Engine::SQLServer (interface to MS SQLServer db)
	Rosetta::Engine::Adabas (interface to Software AG's Adabas db)
	Rosetta::Engine::SAPdb (interface to the SAP open source db; forked from Adabas apparently)
	Rosetta::Engine::Unify (interface to Unify db)
	Rosetta::Engine::Empress (interface to the Empress db)
	Rosetta::Engine::PrimeBase (interface to PrimeBase db)
	Rosetta::Engine::OpenBase (interface to OpenBase db 8.x)
	Rosetta::Engine::FrontBase (interface to FrontBase db)
	Rosetta::Engine::InterBase (binding to Borland InterBase embedded db)
	Rosetta::Engine::Firebird (interface to Firebird db)
	Rosetta::Engine::Solid (interface to Solid db)
	Rosetta::Engine::Cache (interface to InterSystems Cache db)
	Rosetta::Engine::xBase (binding to XBase db accessor library)
	Rosetta::Engine::Ingres (interface to Ingres db)
	Rosetta::Engine::Illustra (interface to Illustra database)
	Rosetta::Engine::Valentina (binding to Paradigma Software's Valentina embedded db) 
	Rosetta::Engine::RelX (binding to relX' embedded db) 
	Rosetta::Engine::4D (interface to 4D db)
	Rosetta::Engine::mSQL (interface to mSQL db)
	Rosetta::Engine::Helix (interface to Helix db)
	Rosetta::Engine::Pick (interface to Pick Systems' db)
	Rosetta::Engine::PointBase (interface to PointBase db, if linking to Java is possible)
	Rosetta::Engine::HSQLDB (interface to HSQLDB db, if linking to Java is possible)
	Rosetta::Engine::FileMaker (interface to FileMaker Pro db)
	Rosetta::Engine::FoxPro (interface to FoxPro db)
	Rosetta::Engine::Access (interface to MS Access db)
	Rosetta::Engine::Paradox (interface to Borland Paradox db)
	Rosetta::Engine::dBase (interface to dBase db)
	Rosetta::Engine::CSV (a database Engine using CSV files for storage)
	Rosetta::Engine::* ... any of the 100+ other databases or services not listed above

=head2 In distribution "Rosetta-Proxy"

I<Some terms seen here are out of date.>

	Rosetta::Proxy::Server (an application on top of RNI implementing a network server)
	Rosetta::Proxy::Client (a "Engine" implementing a network client of the server)
	Rosetta::Proxy::Command (network-safe packed repr of ::Interface::Command obj)
	Rosetta::Proxy::Result (network-safe packed repr of ::Interface::Result obj)

=head2 In a multiplicity of "Rosetta-Emulator-*" distributions

	Rosetta::Emulator::DBI (emulates DBI/DBD::*, but result is more portable)
	Rosetta::Emulator::ODBC (emulates an ODBC module, result more portable)
	Rosetta::Emulator::OCI (emulates an OCI module, result more portable)
	Rosetta::Emulator::* ... like some of the other abstraction modules
	Rosetta::Emulator::*::* (helpers for emulated frameworks of several modules)

=head2 In a multiplicity of "Rosetta-Application-*" distributions

	Rosetta::Application::* ... higher level functionality like: Backup, Restore, Copy, ...

=head2 In unknown distributions

	Rosetta::* ... who knows ...

	Rosetta::Adapter::* ... I like the name so it might be used for something

	RosettaX::* ... unofficial extensions or wrappers to Rosetta are allowed here ...

=head2 In historical posterity distribution "SQL-SyntaxModel-ByTree"

	SQL::SyntaxModel::ByTree (Build SQL::SyntaxModels from multi-dimensional Perl hashes and arrays)
	SQL::SyntaxModel::ByTree::L::en (Localization of SQL::SyntaxModel::ByTree for English)

=head2 In historical posterity distribution "SQL-SyntaxModel-SkipID"

	SQL::SyntaxModel::SkipID (Use SQL::SyntaxModels without inputting Node IDs)
	SQL::SyntaxModel::SkipID::L::en (Localization of SQL::SyntaxModel::SkipID for English)

=head1 OLDER DOCUMENTATION

These paragraphs were more or less the original documentation for high-level
Rosetta concepts, back when each concept was planned to be a separate class of
its own.  They were originally published in Framework.pod since the first
release of the Rosetta distribution (2003-01-05).  Some details you see here
shouldn't be considered accurate.  One portion that was here as late as
2004-02-04, 'Model Modules', has been moved to Language.pod, as of 2004-02-12.

=head2 Interface Modules

=over 4

=item

B<Rosetta::Interface> - This Interface class is inherited by all other Interface
Interface classes, and it provides functionality to talk to or manage Engine modules.
Its main task is to define the execute_command() method, which takes a Command
object saying what should be done next and returns or throws a Result object
saying what actually was done (or what errors there were).  For some command
types, execute_command() may only start the process that needs doing (eg: get a
select cursor), and invoking execute_command() again on the Result object
(which is a subclass) will continue or finish the process (eg: fetch a row). 
Instantiated by itself, this class stores globals that are shared by all
Engines or connections.  Subclasses include: Result, Connection.

=item

B<Rosetta::Command> - This Interface class describes an action that needs
to be done against a database; its objects encapsulate
SQL::SyntaxModel::Command objects and also encapsulates the resolved bind vars,
or live objects like 'Cursor'.  Code using these objects should be doing
something like both calling DBI->prepare() and DBI->execute().  I<See also
SQL::SyntaxModel::Command.>

=item

B<Rosetta::Result> - This Interface class is inherited by all Interface
classes that would be returned from or thrown by an execute_command() method,
and it contains the return values or errors of a Command.  Its main task is to
implement the is_error() and get_error() methods, which say whether the Command
failed or not, and if so then why.  Some commands (eg: 'database_close')
have no other meta-data or data to return, while others do (eg: 'data_select').  
Subclasses include: Connection.

=item

B<Rosetta::Connection> - This Interface class represents a connection
to a database instance, and the simplest database applications use only one.
You instantiate a Connection object by executing a Command of type
'database_open'; that command usually takes 4 arguments, the first of which
is mandatory: 'engine' is a string having the name of the Engine module to use,
which also defines what RDBMS product is being used; 'server' is the name of
the specific database instance to use; 'user' is the username to authenticate
yourself against a multi-user database as; 'pass' is the associated password.

=item

B<Rosetta::Cursor> - This Interface class represents a cursor over a
rowset that is being selected from a database.  You instantiate a Cursor object
by executing a command of type 'data_select'; that command usually takes 1
argument, which is mandatory: 'view' is a View object that describes the select
statement being run, including what columns it has and their datatypes, what
the source tables are, how they are joined, what the row filters are, sort
order, and row limiting or paging.  

=back

=head2 Utility Modules

=over 4

=item

B<Rosetta::Utility::RWViews> - This is a utility class containing common
functionality for multiple Engines.  Given that most, if not all, existing
RDBMS systems don't support updateable views, meaning treating a view like a
table in every way, this class will implement that Rosetta feature, translating
selects, inserts, updates, or deletes against a view into one or more
corresponding actions against the underlying tables that the view interfaces.

=item

B<Rosetta::Utility::SQLBuilder> - This is a utility class containing
common functionality for multiple Engines.  Given that a majority of commonly
used RDBMS systems use SQL as their primary command language, this class will
take care of translating RNI commands into SQL commands.  While a large part of
SQL is implemented in a common way on most SQL-using databases, this class will
take arguments that instruct it how to vary the SQL output to the dialect that
a particular RDBMS uses.  Note that the default SQL being produced will be 
compliant with the ANSI/ISO SQL-2003 standard.

=back

=head2 Engine Modules

=over 4

=item

B<Rosetta::Engine::Generic> - This Engine is a "default catch-all" that I am
providing to get Rosetta up and working quickly with a wide variety of
databases, specifically all those that have a DBI driver (eg, DBD::Oracle) and
are "normal" SQL databases (or are the likes of DBD::ODBC who front "normal"
databases).  This distribution has a dependency in the Rosetta-Utilities
distribution, which handles the meat of the SQL generation (and parsing in the
case of reverse-engineering some schemas); it also, obviously, has a dependency
on DBI and one or more DBD modules.

=item

B<Rosetta::Engine::SQLite> - This class embeds the public domain SQLite RDBMS,
and will serve as a default (though separately distributed) Engine for Rosetta.
It is small, powerful, easy to install and use, and implements the most
important parts of the RNI, including Unicode, portability, transactions, and
subselects.  This Engine is intended mainly for programs that are used by one
person at a time, as locks will grab the whole database.  Given that the actual
database is embedded into the Engine, we simply use the latest version
available at the time of each Engine update, so mention of version ranges being
supported or not is not applicable.  That said, v2.8.15 is the current stable
branch, and v3.0.4 is the current beta branch, which will move into production
within a month or two.

=item

B<Rosetta::Engine::Oracle> - This class implements an Engine for talking to
Oracle 8.x, 9.x, 10.x databases.  Note that Oracle 9 is the first version of the
Oracle database that runs under Mac OS X (10.2 and later).  Oracle versions 
before 8.x, like 7.3, will not be supported unless there is a great demand.

=item

B<Rosetta::Engine::PostgreSQL> - This class implements an Engine for talking to
PostgreSQL databases.  It is intended to be used only with PostgreSQL versions
7.4.3 and later, with version 8.0.0 or greater being strongly recommended. That
said, which version you should use depends on your stage of development.
PostgreSQL 8.0.0 officially went beta on 2004.08.10, while the officially
stable 7.4.3 was released on 2004.06.15.  Support for 7.3.x in this module will
be present in the short term, but it is deprecated.  7.2.x and earlier will not
be supported at all, without great demand.

=item

B<Rosetta::Engine::MySQL> - This class implements an Engine for talking to
MySQL databases.  It is intended to be used only with MySQL versions 4.0.20 and
later, with version 4.1.3 or greater being strongly recommended.  That said,
which version you should use depends on your stage of development.  MySQL AB
had declared the 4.0.x series to be production quality at v4.0.12 (2003.03.15),
and since then this line had over a year's worth of bug-fix improvements. 
MySQL AB had declared the 4.1.x series to be beta quality at v4.1.3
(2004.06.28), and previously was at alpha quality at v4.1.0 (2003.04.10); they
initially said the 4.1.x line would be production ready 8 months after its
alpha release.  MySQL AB provided a preview release of the 5.0.x line on
2003.12.22, which is v5.0.0; at the same time that the 4.1.x line was declared
stable, the 5.0.x line was declared alpha, without a version increment; they
initially said 5.0.x would be production ready 6 months after 4.1.x was. 
Support for 3.23.x in this module will be present in the short term, but it is
deprecated.  3.22.x and earlier will not be supported at all, without great
demand.

=item

B<Rosetta::Engine::OpenBase> - This class implements an Engine for talking to
OpenBase 8.0.3 databases.  v7.x and earlier won't be supported without demand.

=back

All other databases in common use should be supported as well; some in the
above module list are products that I have used personally; I need to research
others to know what versions exist or are stable or are in common use.  Other
RDBMS products include: Sybase, DB2, SQL-Server, FrontBase, Valentina,
Informix, and others.

=head2 Miscellaneous Modules From Afar

In this context, "Wrapper" is a type of Rosetta extension that sits between 
the application and the RNI, such as Emulators.  But Wrappers take many forms, 
most of which will not be included with this distribution.

One form of Wrapper is a value-added extension, possibly more
application-specific, such as an interpreter for data dictionaries.  For
example, a data dictionary could say that an application is composed of screens
or forms that are related in a certain way; each screen would contain several
controls of various types, and some controls may correspond to specific columns
in database tables. The module in question would determine from the data
dictionary what needs to be retrieved from the database to support a particular
screen, and ask the Interface modules to go get it.  Similarly, if the application
user edits data on the screens that should then be saved back to the database,
the Wrapper module would ask the Interface modules to save it. On the other side of
things, it is quite possible that the data dictionary for the application is
itself stored in the database, and so the Interface modules can be asked to fetch
portions of it as the Wrapper module requires.

Another form of Wrapper is an interface customizer or simplifier.  if you know
that certain details of your commands to Interface will always be the same, or you
just like to express your needs in a different way, you can take care of the
default values in a wrapper module, so that the rest of your application simply
has to provide inputs that aren't always the same.

Another form of Wrapper is a data parser or serializer.  For example, to convert
database output to XML or convert XML to a database command (although, certain
kinds of XML processing may be better implemented in the Interface/Engine layers for
performance reasons, but if so it would still be an extension).

Another form of Wrapper is a command parser for various SQL dialects.  For
example, if you want to quickly port an application, which already includes SQL
statements that are tailored to a specific database product, to a different
database for which it is incompatible, a Wrapper module could parse that statement
into the object representation that Interface uses.  This is effectively an
SQL-to-SQL translator.  I would expect that, citing reasons of performance or
application code simplicity, one wouldn't want to use this functionality
long-term, but replace the SQL with Interface object definitions later.

Finally, one could also make Wrappers which emulate other database abstraction
solutions for similar reasons to the above, which is a different type of quick
porting.  Since the intended feature set of Rosetta should be a superset
of existing solutions' feature sets, it should be possible to emulate them with
it.  

=head1 OLDER EXAMPLE PROGRAM

The following sample code is more or less the original SYNOPSIS documentation
in Framework.pod since the first release of the Rosetta distribution
(2003-01-05); it was moved down here as of 2004-02-23.  Some details you see
here shouldn't be considered accurate; the new SYNOPSIS in Rosetta.pm is
loosely derived from this, and that is up to date.

=head2 Content of settings file "survey_prefs.pl", used by script below:

	my $rh_prefs = {
		database_engine => 'Rosetta::Engine::MySQL',
		database_open_args => {
			server => 'survey1',
			user => 'joebloe',
			pass => 'fdDF9X0sd7zy',
		},
		question_list => [
			{
				visible_title => "What's your name?",
				type => 'str',
				name => 'name',
				is_required => 1,
			}, {
				visible_title => "What's the combination?",
				type => 'int',
				name => 'words',
			}, {
				visible_title => "What's your favorite colour?",
				type => 'str',
				name => 'color',
			},
		],
	};

=head2 Content of a simple CGI script for implementing a web survey:

	#!/usr/bin/perl
	use strict;
	use warnings;

	&script_main();

	sub script_main {
		my $base_url = 'http://'.($ENV{'HTTP_HOST'} || '127.0.0.1').$ENV{'SCRIPT_NAME'};
		my ($curr_mode) = $ENV{'QUERY_STRING'} =~ m/mode=([^&]*)/;

		my $form_data_str = '';
		read( STDIN, $form_data_str, $ENV{'CONTENT_LENGTH'} );
		chomp( $form_data_str );
		my %form_values = ();
		foreach my $pair (split( '&', $form_data_str )) {
			my ($key, $value) = split( '=', $pair, 2 );
			next if( $key eq "" );
			$key =~ tr/+/ /;
			$key =~ s/%([0-9a-fA-F]{2})/pack("c",hex($1))/ge;
			$value =~ tr/+/ /;
			$value =~ s/%([0-9a-fA-F]{2})/pack("c",hex($1))/ge;
			$form_values{$key} = $value;
		}

		my $fn_prefs = 'survey_prefs.pl';

		print
			"Status: 200 OK\n",
			"Content-type: text/html\n\n",
			"<html><head>\n",
			"<title>Simple Web Survey</title>\n",
			"</head><body>\n",
			"<p><a href=\"$base_url?mode=install\">Install Schema</a>\n",
			" | <a href=\"$base_url?mode=remove\">Remove Schema</a>\n",
			" | <a href=\"$base_url?mode=fillin\">Fill In Form</a>\n",
			" | <a href=\"$base_url?mode=report\">See Report</a></p>\n",
			"<hr />\n",
			"<form method=\"POST\" action=\"$base_url?mode=$curr_mode\">\n",
			"<p>\n",
			(&script_make_screen( $fn_prefs, $curr_mode, \%form_values )),
			"</p>\n",
			"<p><input type=\"submit\" name=\"OK\" value=\"Do It Now\" /></p>\n",
			"</form>\n",
			"</body></html>\n";
	}

	sub script_make_screen {
		my ($fn_prefs, $curr_mode, $form_values) = @_;

		my $prefs = do $fn_prefs;
		unless( ref( $prefs ) eq 'HASH' ) {
			return( "Error: can't obtain required preferences hash from '$fn_prefs': ".
				(defined( $prefs ) ? "result not a hash ref, but '$prefs'" : 
				$@ ? "compilation or runtime error of '$@'" : $!) );
		}

		eval {
			require Rosetta; # also compiles SQL::SyntaxModel
		};
		if( $@ ) {
			return( "Error: can't compile Rosetta modules: $@" );
		}

		my $interface = Rosetta->new_interface();
		$interface->throw_error( 0 ); # on error, ret result obj, do not throw exception

		my $dbh = $interface->execute_command( {
			'type' => 'database_open',
			'engine' => $prefs->{database_engine},
			'args' => $prefs->{database_open_args}, # includes server name, user/pass
		} );
		if( $dbh->is_error() ) {
			return( "Error: can't open database: ".$dbh->get_error() );
		}

		my $html_output = &script_while_opened( $prefs, $dbh, $curr_mode, $form_values );

		my $rv = $dbh->execute_command( {
			'type' => 'database_close',
		} );
		if( $rv->is_error() ) {
			return( "Error: can't close database: ".$rv->get_error() );
		}

		return( $html_output );
	}

	sub script_while_opened {
		my ($prefs, $dbh, $curr_mode, $form_values) = @_;

		my $questions = $prefs->{question_list};
		unless( ref( $questions ) eq 'ARRAY' and scalar( @{$questions} ) > 0 ) {
			return( "Error: no survey question list defined in prefs file" );
		}

		my $dd_table = SQL::SyntaxModel->new_table( 'survey_data' );

		foreach my $question (@{$questions}) {
			unless( ref( $question ) eq 'HASH' and $question->{visible_title} ) {
				return( "Error: invalid question defined in prefs file" );
			}
			$dd_table->add_column( { 
				'name' => $question->{name},
				'data_type' => { 'base_type' => $question->{type}, },
				'is_req' => $question->{is_required},
			} ) or return( "Error: invalid question defined in prefs file" );
		}

		if( $curr_mode eq 'install' ) {
			return( &script_do_install( $dbh, $dd_table, $questions, $form_values ) );
		}

		if( $curr_mode eq 'remove' ) {
			return( &script_do_remove( $dbh, $dd_table, $questions, $form_values ) );
		}

		if( $curr_mode eq 'fillin' ) {
			return( &script_do_fillin( $dbh, $dd_table, $questions, $form_values ) );
		}

		if( $curr_mode eq 'report' ) {
			return( &script_do_report( $dbh, $dd_table, $questions, $form_values ) );
		}

		return( "This is a simple demo.  Click on the menu items to do them." );
	}

	sub script_to_install {
		my ($dbh, $dd_table, $questions, $form_values) = @_;

		unless( $form_values->{OK} ) {  
			# user is seeing screen for first time (did not click 'OK' button)
			return( join( "", 
				"<h1>Install Schema</h1>\n",
				"<p>Do you want to install new schema to store answers for ", 
				"the following questions?</p>\n",
				"<ol>\n",
				(map { "<li>".$_->{visible_title}."</li>\n" } @{$questions}),
				"</ol>\n",
			) );
		}

		# user saw screen and clicked the 'OK' button, so try to install;
		# the following makes a Command of type 'table_create' and executes it

		my $rv = $dbh->execute_command( $dd_table->new_command_create() );
		if( $rv->is_error() ) {
			return( "Error: can't create survey table: ".$rv->get_error() );
		}

		return( "The new schema was successfully created." );
	}

	sub script_to_remove {
		my ($dbh, $dd_table, $questions, $form_values) = @_;

		unless( $form_values->{OK} ) {  
			# user is seeing screen for first time (did not click 'OK' button)
			return( join( "", 
				"<h1>Remove Schema</h1>\n",
				"<p>Do you want to remove existing schema to store answers for ", 
				"the following questions?</p>\n",
				"<ol>\n",
				(map { "<li>".$_->{visible_title}."</li>\n" } @{$questions}),
				"</ol>\n",
			) );
		}

		# user saw screen and clicked the 'OK' button, so try to destroy;
		# the following makes a Command of type 'table_destroy' and executes it

		my $rv = $dbh->execute_command( $dd_table->new_command_destroy() );
		if( $rv->is_error() ) {
			return( "Error: can't remove survey table: ".$rv->get_error() );
		}

		return( "The new schema was successfully removed." );
	}

	sub script_to_fillin {
		my ($dbh, $dd_table, $questions, $form_values) = @_;

		unless( $form_values->{OK} ) {  
			# user is seeing screen for first time (did not click 'OK' button)
			return( join( "", 
				"<h1>Fill In Form</h1>\n",
				"<p>Please answer the following questions.  ",
				"Those marked with a '*' are required.</p>\n",
				(map { 
						'<p>'.($_->{is_required} ? '*' : '').$_->{visible_title}.":".
						'<input type="text" name="'.$_->{name}.'" /></p>'."\n"
					} @{$questions}),
			) );
		}

		# user saw screen and clicked the 'OK' button, so try to fillin;
		# the following makes a Command of type 'data_insert' and executes it
		my $dd_view = SQL::SyntaxModel->new_view( $dd_table );
		my $rv = $dbh->execute_command( $dd_view->new_command_insert( $form_values ) );
		if( $rv->is_error() ) {
			return( "Error: can't save form values in database: ".$rv->get_error() );
		}

		return( "Your form submission was saved successfully." );
	}

	sub script_to_report {
		my ($dbh, $dd_table, $questions, $form_values) = @_;

		# the following makes a Command of type 'data_select' and executes it
		my $dd_view = SQL::SyntaxModel->new_view( $dd_table );
		my $cursor = $dbh->execute_command( $dd_view->new_command_select() );
		if( $cursor->is_error() ) {
			return( "Error: can't fetch form values from database: ".$cursor->get_error() );
		}
		my $rowset = $cursor->get_all_rows();

		my @html_output = (
			"<h1>See Report</h1>\n",
			"<p>Here are the answers that previous visitors gave:</p>\n",
			"<table>\n",
			"<tr>\n",
			(map { "<th>".$_->{visible_title}."</th>\n" } @{$questions}),
			"</tr>\n",
		);
		my @question_names = map { $_->{name} } @{$questions};
		foreach my $row (@{$rowset}) {
			push( @html_output, 
				"<tr>\n",
				(map { "<td>".$row->{$_}."</td>\n" } @question_names),
				"</tr>\n",
			);
		}
		push( @html_output, "</table>\n" );

		return( join( "", @html_output ) );
	}

	1;

=head1 SEE ALSO

Rosetta and the various other modules mentioned in its SEE ALSO.

=cut
