sednaobject - Pythonic interface to Sedna XML Database

Jim Washington jwashin at
Wed Apr 9 14:58:18 CEST 2008

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.



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

- Jim Washington

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