Dear All, v0.2 of versioned domain model is now finally done -- it was 95% complete in Feb but it has taken another 3 months to iron out the last bugs and polish up!
Apart from being a concrete implementation of a system for versioning data(bases) -- and therefore important for efforts to do more collaborative development of data [1] -- it is also a crucial piece of infrastructure for various of our current and future projects such as CKAN, Microfacts/Weaving History, and Public Domain Works. Regards, Rufus [1]:<http://blog.okfn.org/2007/02/20/collaborative-development-of-data/> ## Versioned Domain Model (v0.2) with Support for SQLAlchemy Versioned Domain Model (vdm) is a package which allows you to 'version' your domain model in the same way that source code version control systems such as subversion allow you version your code. In particular, versioned domain model versions a complete model and not just individual domain objects (for more on this distinction see below). At present the package is provided as an extension to SQLAlchemy and SQLObject (with an extension to Elixir in progress). ### Getting It Either via easy_install:: $ easy_install vdm Or from subversion at:: http://knowledgeforge.net/ckan/svn/vdm/trunk ### A Full Versioned Domain Model To permit 'atomic' changes involving multiple objects at once as well as to facilitate domain object traversal it is necessary to introduce an explicit 'Revision' object to represent a single changeset to the domain model. One also needs to introduce the concept of 'State'. This allows us to make (some) domain objects stateful, in particular those which are to be versioned (State is necessary to support delete/undelete functionality as well as to implement versioned many-to-many relationships). For each original domain object that comes versioned we end up with 2 domain objects: * The 'continuity': the original domain object. * The 'version/revision': the versions/revisions of that domain object. Often a user will never need to be concerned (explicitly) with the version/revision object as they will just interact with the original domain object, which will, where necessary, 'proxy' requests down to the 'version/revision'. To give a flavour of all of this here is a pseudo-code example:: # NB: Book and Author are domain objects which has been made # versioned using the vdm library # # we need a session of some kind to track which objects have been changed # each session then has a single revision rev1 = Revision(author='me') session.revision = rev1 # typo! b1 = Book(name='warandpeace', title='War and Peacee') b2 = Book(name='annakarenina', title='Anna') b3 = Book(name='warandpeace') a1 = Author(name='tolstoy') # this is just shorthand for ending this revision and saving all changes # this may vary depending on the implementation rev1.commit() timestamp1 = rev1.timestamp # some time later rev2 = Revision(author='me') session.revision = rev2 b1 = Book.get(name='warandpeace') # correct typo b1.title = 'War and Peace' # add the author a1 = Author.get(name='tolstoy') b1.authors.append(a1) # duplicate item so delete b3.delete() rev2.commit() # some time even later rev1 = Revision.get(timestamp=timestamp1) b1 = Book.get(name='warandpeace') b1 = b1.get_as_of(rev1) assert b1.title == 'War and Peacee' assert b1.authors == [] # etc ### More Information For more information see the documentation in the package repository at: <http://knowledgeforge.net/ckan/svn/vdm/trunk/> _______________________________________________ okfn-discuss mailing list [email protected] http://lists.okfn.org/cgi-bin/mailman/listinfo/okfn-discuss
