NAME

Muldis::Rosetta - Full-featured truly relational DBMS in Perl

VERSION

This document is Muldis::Rosetta version 0.16.0.

DESCRIPTION

The Muldis Rosetta DBMS framework is a powerful but elegant system, which makes it easy to create and use relational databases in a very reliable, portable, and efficient way. This "Rosetta" file provides a 10,000 mile view of the Muldis Rosetta framework as a whole, and the detail documentation for each component is included with that component. The distribution containing this "Rosetta" file is the Muldis Rosetta core distribution.

Loosely speaking, the Muldis Rosetta framework at large is like the Perl DBI framework at large, so if you know how to use the Perl DBI to work with databases, it should be easy enough to apply that knowledge to using Muldis Rosetta to work with databases. Like the Perl DBI, Muldis Rosetta has separately distributable core/API, implementation, and extension distributions. Like an implementation ("driver") of the Perl DBI, an implementation ("engine") of Muldis Rosetta works according to the command design pattern; its API is very minimalistic and mainly serves to process arbitrary "commands" through a single routine or three. Also like the Perl DBI, Muldis Rosetta does not strictly require that said commands are written in any particular programming language. Unlike the Perl DBI, which typically takes commands in various implementation-specific dialects of SQL that are mutually incompatible to a large degree, Muldis Rosetta typically takes commands in various dialects of Muldis D that are highly standardized across implementations and have little or no mutual incompatability. See the separate all-documentation distribution Muldis::D for the formal definition of the Muldis D language, which Muldis Rosetta also serves as the reference implementation of.

The minimal core of the Muldis Rosetta framework, the one component that probably every program would use, is the Muldis::Rosetta::Interface file. It defines a small set of roles/classes that comprise a common API (that processes Perl Hosted Data Muldis D commands) for Muldis Rosetta implementations to do and which applications invoke, called the Muldis Rosetta Native Interface (or MRNI). For the most part, Interface just defines shims and it can only be used when they are subclassed by an implementation. In the Perl DBI framework analogy, Interface corresponds to the DBI module itself. An implementation is called a Muldis Rosetta Engine or Engine.

Thanks largely to the use of Muldis D as its primary command language, MRNI is rigorously defined, such that there should be no ambiguity when trying to invoke or implement it, and so an application written to it should behave identically no matter which conforming Engine is in use.

The maximal core of the Muldis Rosetta framework, everything else of substance in the same distribution as the minimal core (and this "Rosetta" file), comprises 2 additional components. The first is Muldis::Rosetta::Engine::Example, a self-contained and pure-Perl reference implementation of Muldis Rosetta. The second is Muldis::Rosetta::Validator, a common comprehensive test suite for Muldis Rosetta implementations. Together, these components make it possible for the Muldis Rosetta core distribution to be completely testable on its own. It is therefore also feasible for an application to use the Muldis Rosetta core in isolation from further framework components, though doing so isn't recommended for production use since Example is kept simple on purpose and doesn't scale well.

Muldis Rosetta, by way of using the Muldis D language, incorporates a complete and uncompromising implementation of "The Third Manifesto" (TTM), a formal proposal by Christopher J. Date and Hugh Darwen for a solid foundation for data and database management systems (DBMSs); like Edgar F. Codd's original papers, TTM can be seen as an abstract blueprint for the design of a DBMS and the language interface to such a DBMS. Muldis D is a high-level programming language which is computationally complete (and industrial strength) and has fully integrated database functionality; it satisfies TTM's definition of a "D" language. The main web site for TTM is http://www.thethirdmanifesto.com/, and its authors have also written several books and papers and taught classes on the subject over the last 35+ years, along with Codd himself (some are listed in the separately distributed Muldis::D::SeeAlso documentation file). Note that the Muldis Rosetta documentation will be focusing mainly on how Muldis Rosetta itself works, and will not spend much time in providing rationale; you can read TTM itself and various other external documentation for much of that.

This documentation is pending.

While it is possible that one could write a self-contained application in Muldis D and compile that into its own executable, in practice one would normally just write some components of their application in Muldis D (as either named modules or anonymous routines) and write the rest of the application in their other language(s) of choice. Assuming the main application is written in Perl, it is the Muldis::Rosetta::Interface file which provides the glue between your Perl code and your Muldis D code; "Muldis::Rosetta::Interface" implements a virtual machine that is embedded in your Perl application and in which the Muldis D code runs (it is analogous to the Perl interpreter itself, which provides a virtual machine in which Perl code runs).

A Muldis::Rosetta::Interface::Machine object represents a single active Muldis Rosetta virtual machine; it has a spartan DBI-inspired set of methods which you use to compile/prepare and/or invoke/execute Muldis D statements and routines within the virtual machine, input data to it, and output data from it.

You can create more than one Machine object at a time, and they are essentially all isolated from each other, even if more than one uses the same Engine class to implement it; that is, multiple Machine objects will not have references to each other at a level visible in the Muldis Rosetta Native Interface, if at all. To account for situations where multiple Machine objects want to use the same external resources, such as a repository file on disk, it is expected that the Engines will employ appropriate measures such as system-managed locks so that resource corruption or application failure is prevented. Also, Muldis Rosetta should be thread safe and/or savvy in the future, but for now it officially is not and you should not share Muldis Rosetta objects between multiple threads, nor have objects in separate threads try to access the same external resources.

Muldis Rosetta does not use any dialect of SQL in its native API (unlike many other DBMS products) because SQL is more ambiguous and error-prone to use, and it is less expressive. While Muldis D is very different from SQL, it is fully capable of modeling any statements about anything in the real world accurately, and it can support a complete SQL emulation layer on top of it, so that your legacy applications can be migrated to use the Muldis Rosetta DBMS with little trouble. Likewise, emulation layers for any other programming language can be supported, such as Tutorial D or XQuery or FoxPro or dBase.

One distinctive feature of a Muldis Rosetta DBMS (compared to a typical other vendor's DBMS) is that data definition statements are structured fundamentally as standard data manipulation statements but that the target relation variables are system catalog relation variables rather than user-defined relation variables. In SQL terms, you create or alter tables by adding or updating their "information schema" records, which in SQL are read-only, not only by using special 'create' or 'alter' statements.

Each Muldis Rosetta Engine has the complete freedom to implement the Muldis Rosetta DBMS and Muldis D however it likes; all Muldis Rosetta cares about is that the user interface and behaviour conform to its preconceptions.

For production use, there should be a wide variety of third party Engine modules that become available over time. One plan being favored is that the new (under development) enterprise-strength and Perl implemented database server named Genezzo (see also http://www.genezzo.com/) will evolve to implement the Muldis Rosetta DBMS natively, and be the back-end which is recommended above all others for production use.

Most of the other (near term) third party Engines will likely just map Muldis Rosetta's rigorously defined API onto a pre-existing quasi-relational database manager (such as SQLite, PostgreSQL, MySQL, Firebird, Teradata, Oracle, Sybase, SQL Server, Informix, DB2, OpenBase, FrontBase, etc). Given this fact, Muldis Rosetta's most prominent feature is that it provides a common API for access to those databases, each of which takes a different SQL or quasi-SQL dialect. An application written to it should easily port to alternative relational database engines with minimal effort.

This might seem strange to somebody who has not tried to port between databases before, especially given that the Perl DBI purports to provide "Database Independence". However, the level of DBI's provided independence is Database Driver Independence, and not Database Language Independence. To further demonstrate the difference, it is useful to compare the DBI and Muldis Rosetta. Such documentation is currently absent.

In the context of a Muldis Rosetta implementation over the Perl DBI, if one were to categorize Muldis Rosetta among other Perl modules, it could reasonably be called a database abstraction layer; but it should not be called a Perl object persistence layer, as that is a different paradigm.

FEATURE SUPPORT VALIDATION

The Muldis Rosetta Native Interface declares accessors for a large number of actual or possible database features, any of which your application can invoke, and all of which each Muldis Rosetta Engine would ideally implement or interface to.

In reality, however, all Engines or underlying databases probably don't support some features, and if your application tries to invoke any of the same features that an Engine you are using doesn't support, then you will have problems ranging from immediate crashes/exceptions to subtle data corruption over time.

As an official quality assurance (QA) measure, Muldis Rosetta provides a means for each Engine to programmatically declare which features it does and does not support, so that code using that Engine will know so in advance of trying to use said features. Feature support declarations are typically coarse grained and lump closely similar things together, for simplicity; they will be just as fine grained as necessary and no finer (this can be changed over time). See the features() method, which is how you read the declarations.

One benefit of this QA feature is that, after you have written your application and it is working with one Engine/database, and you want to move it to a different Engine/database, you can determine at a glance which alternatives also support the features you are using. Note that, generally speaking, you would have to be using very proprietary features to begin with in order for the majority of Muldis Rosetta Engines/databases to not support the application outright.

Another benefit of this QA feature is that there can be made a common comprehensive test suite to run against all Engines in order to tell that they are implementing the Muldis Rosetta interface properly or not; said test suite will be smart enough to only test each Engine's compliance for those features that the Engine claims to support, and not fail it for non-working features that it explicitly says it doesn't support. This common test suite will save each Engine maker from having to write their own module tests. It 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. Please see the Muldis::Rosetta::Validator module(s), which implements this test suite.

SEE ALSO

The separate all-documentation distribution Muldis::D is the formal definition of the Muldis D language which Muldis Rosetta is based on.

The Perl module Muldis::Rosetta::Validator is bundled with Muldis Rosetta and can be used to test Muldis Rosetta Engines.

The Perl module Muldis::Rosetta::Engine::Example is bundled with Muldis Rosetta and implements a self-contained reference implementation of a Muldis Rosetta Engine.

Go to the Muldis::Rosetta::SeeAlso file for the majority of external references.

AUTHOR

Darren Duncan (darren@DarrenDuncan.net)

LICENSE AND COPYRIGHT

This file is part of the Muldis Rosetta framework.

Muldis Rosetta is Copyright © 2002-2010, Muldis Data Systems, Inc.

http://www.muldis.com/

Muldis Rosetta is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License (LGPL) as published by the Free Software Foundation (http://www.fsf.org/); either version 3 of the License, or (at your option) any later version. You should have received a copy of the LGPL as part of the Muldis Rosetta distribution, in the files named "LICENSE/LGPL" and "LICENSE/GPL" (the LGPLv3 is defined as the terms of the GPLv3 plus extra permissions); if not, see http://www.gnu.org/licenses/.

If it is not feasible for you to employ Muldis Rosetta subject to the terms of the LGPL, then the copyright holder of Muldis Rosetta can provide you a customized proprietary license, often at no cost, so that it is still possible for you to employ Muldis Rosetta to meet your needs.

Any versions of Muldis 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. Muldis 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. However, for an additional fee, the copyright holders of Muldis Rosetta can sell you a warranty for it.

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

TRADEMARK POLICY

MULDIS and MULDIS MULTIVERSE OF DISCOURSE are trademarks of Muldis Data Systems, Inc. (http://www.muldis.com/). The trademarks apply to computer database software and related services. See http://www.muldis.com/trademark_policy.html for the full written details of Muldis Data Systems' trademark policy.

The word MULDIS is intended to be used as the distinguishing brand name for all the products and services of Muldis Data Systems. So we would greatly appreciate it if in general you do not incorporate the word MULDIS into the name or logo of your website, business, product or service, but rather use your own distinct name (exceptions appear below). It is, however, always okay to use the word MULDIS only in descriptions of your website, business, product or service to provide accurate information to the public about yourself.

If you do incorporate the word MULDIS into your names anyway, either because you have permission from us or you have some other good reason, then: You must make clear that you are not Muldis Data Systems and that you do not represent Muldis Data Systems. A simple or conspicuous disclaimer on your home page and product or service documentation is an excellent way of doing that.

Please respect the conventions of the Perl community by not using the namespace Muldis:: at all for your own works, unless you have explicit permission to do so from Muldis Data Systems; that namespace is mainly just for our official works. You can always use either the MuldisX:: namespace for related unofficial works, or some other namespace that is completely different. Also as per conventions, its fine to use Muldis within a Perl package name where that word is nested under some other project-specific namespace (for example, Foo::Storage::Muldis_Rosetta or Bar::Interface::Muldis_Rosetta), and the package serves to interact with a Muldis Data Systems work or service.

If you have made a language variant or extension based on the Muldis D language, then please follow the naming conventions described in the VERSIONING ("VERSIONING" in Muldis::D) documentation of the official Muldis D language spec.

If you would like to use (or have already used) the word MULDIS for any use that ought to require permission, please contact Muldis Data Systems and we'll discuss a way to make that happen.

ACKNOWLEDGEMENTS

None yet.

FORUMS

Several public email-based forums exist whose main topic is all implementations of the Muldis D language, especially the Muldis Rosetta reference implementation, but also the Set::Relation module. All of these you can reach via http://mm.DarrenDuncan.net/mailman/listinfo; go there to manage your subscriptions to, or view the archives of, the following:

muldis-db-announce@mm.DarrenDuncan.net

This low-volume list is mainly for official announcements from the Muldis Rosetta developers, though developers of Muldis Rosetta extensions can also post their announcements here. This is not a discussion list.

muldis-db-users@mm.DarrenDuncan.net

This list is for general discussion among people who are using Muldis Rosetta, which is not concerned with the implementation of Muldis Rosetta itself. This is the best place to ask for basic help in getting Muldis Rosetta installed on your machine or to make it do what you want. You could also submit feature requests or report perceived bugs here, if you don't want to use CPAN's RT system.

muldis-db-devel@mm.DarrenDuncan.net

This list is for discussion among people who are designing or implementing the Muldis Rosetta core API (including Muldis D language design), or who are implementing Muldis Rosetta Engines, or who are writing core documentation, tests, or examples. It is not the place for non-implementers to get help in using said.

An official IRC channel for Muldis D and its implementations is also intended, but not yet started.

Alternately, you can purchase more advanced commercial support for various Muldis D implementations, particularly Muldis Rosetta, from its author by way of Muldis Data Systems; see http://www.muldis.com/ for details.

cpanm Muldis::Rosetta

perl -MCPAN -e shell
install Muldis::Rosetta