Extension:Page Schemas

Page Schemas is a MediaWiki extension that allows for defining all the schema information about a "class", or data type - for naming, display, data input, and browsing - within a single piece of XML contained within a category page. This XML then is used to generate all the necessary additional pages needed to put the schema into effect, such as template pages and, for instance, if Semantic Forms is installed, form pages. The XML can be created and edited via a helper form, preventing users from having to generate or modify it manually.

Page Schemas allows other extensions to define their own fields to add to the XML, using hooks. Currently, the following extensions hook into Page Schemas:
 * Semantic MediaWiki
 * Semantic Forms
 * Semantic Drilldown
 * Semantic Internal Objects

Special pages
Page Schemas defines two pages that can show up as tabs on category pages: "Edit schema" (which appears as "Create schema" if no schema exists yet) and "Generate pages". "Edit schema" allows for creating or editing the XML via the helper form, while "Generate pages" provides a button that lets the administrator create the template(s), semantic properties, form etc. automatically from the XML definition. "Generate pages" also includes checkboxes for each of the pages to be generated, to let administrators choose not to override certain wiki pages that already exist.

Any user who is allowed to edit a certain category page will see the "Edit schema/Create schema" tab for that category, and will be allowed to use that page to modify the schema.

In order to generate pages, a user must have the 'generatepages' permission. By default, this permission is given only to members of the 'sysop' user group. You can add to or modify the set of allowed users, though, by modifying the $wgGroupPermissions array in LocalSettings.php. To enable all registered users to generate pages from the schema, for instance, you would add the following:

Code and download
You can download the Page Schemas code, in .tgz format, here.

You can also download the code via Git from the MediaWiki source code repository. From a command line, you can call the following:

To view the code online, including version history for each file, go here.

Installation
After you've obtained a 'PageSchemas' directory, place this directory within the main MediaWiki 'extensions' directory. Then, in the file 'LocalSettings.php' in the main MediaWiki directory, add the following line:

Tutorial video
You can see a screencast video for Page Schemas created by Yury Katkov, explaining how it's used and why it can be useful, here.

Sample XML structure
Here is some sample XML, to be contained within a page called "Category:Cities", used to define the schema for pages within that category. This section defines the name of the form, and information for a single field of that class, "Population".

Importing into Page Schemas
There is currently one utility that can import an outside data structure into Page Schemas format:
 * db-to-smw-page-schemas, a script in Node.js that queries a database's schema and generates corresponding category pages with Page Schemas XML.

Author
Page Schemas was created by Ankit Garg as part of the 2011 Google Summer of Code, and was mentored by Yaron Koren. It is currently maintained by Yaron Koren. Parts of it are based on the TemplateInfo extension, by Yaron Koren and Roan Kattouw.

Version history
Page Schemas is currently at version 0.3.1.

The version history for Page Schemas is:
 * 0.1 - August 23, 2011 - initial version
 * 0.2 - October 13, 2011 - overhaul; many changes to display and code structure
 * 0.3 - October 25, 2011 - extensions hook into Page Schemas via a single hook and a subclass, instead of a variety of hooks; various other changes
 * 0.3.1 - August 24, 2012 - template display format can be selected; various small fixes and improvements

Roadmap
Features and improvements that it would be great to add to Page Schemas in the future include:
 * Adding more options to the schema, such as support for the "standard inputs" in Semantic Forms like the free text input.
 * Allowing Semantic Forms to use the Page Schemas XML directly when generating a form, instead of requiring a separate form definition.
 * Support for subobjects instead of, or in addition to, Semantic Internal Objects.
 * Ability to export/import data structure files in formats such as UML and SQL to/from the Page Schemas XML format.
 * Making use of the proposed ContentHandler for storing XML natively, instead of in a wiki page, if/when it gets added to MediaWiki.

There are no immediate plans to add any of these, however.