I've put out a new alpha (0.10alpha2) of zif.sedna, a Python adapter to Sedna, a multi-user XML database, at the Python Cheese Shop.

The new alpha has a start at objectifying XML from the Sedna database in a manner kind of like sqlobject does for SQL. The aim is to make easy, pythonic CRUD (create, read, update, delete) operations for the XML store. Push data in, get data back out.

sednaobject, now included in zif.sedna, provides three classes.

First is SednaXQuery, which gives you list-like semantics for the results of any arbitrary XQuery or XPath expression. You init it with a Sedna cursor, a query statement, and an optional parser method. Then, you can iterate, or obtain items by index or slice. If you do not provide a parser, you get items as unicode strings.

Second is SednaContainer, which behaves like a SednaXQuery, except it is read-write. Like SednaXQuery, you init it with a cursor, a query statement, and an optional parser method. The query statement must refer to exactly one element in the database. This is the container, and you can obtain and replace items in the container by index. Slicing works for retrieval, and append, remove, insert, and del work as per the elementtree API.

Third is SednaObjectifiedElement, which also operates on a single element in the database. SednaObjectifiedElement is a thin wrapper around lxml.objectify. Alter the item with the objectify API, and save(). Thanks, lxml team, for making this really easy!

Since, in XML, an element is an element is an element, you can use the second and third sednaobject classes on any element in the database. Which you would use in a situation depends on the aspect you are interested in at the moment.

I see Sedna as an attractive middle ground between SQL databases and object databases like ZODB. Data size is practically unlimited. You can alter a small portion of a data set transactionally, in a multi-user environment, without a full rewrite of the data. Like SQL databases, it uses a query language to obtain and format just the data you want, from anywhere in the database. XQuery has nice built-in functionality for counting, filtering, reordering, doing math, etc., on items. Like ZODB, you can store and retrieve items of arbitrary complexity without too much fuss. A Sedna database can have multiple XML documents and multiple 'collections' of (similar) documents that can be queried together or separately.

The Sedna team just released version 3.0 of the Sedna server, which has improved speed and reliability. 3.0 now runs on Mac OSX, in addition to x86 Linux and Win2K/XP.

zif.sedna with sednaobject version 0.10 is alpha, so interfaces can and probably will change. The included doctests all pass using a Sedna 2.x server. I have not included the new features of 3.0 (e.g., faster, read-only queries) yet. Testing with a 3.0 server results in a single harmless failure. Speed? I'm getting 60-70 single-query transactions per second through Pylons on a 2Ghz Opteron. Transaction speed of course depends on how many queries are in the transaction and what the queries do.

zif.sedna: http://pypi.python.org/pypi/zif.sedna/

Sedna: http://modis.ispras.ru/sedna/

I am currently the sole developer for zif.sedna. Feedback is welcome.

- Jim Washington