OData: Open for Comments at OASIS

Browsing around this morning I noticed that on Friday (25th Jan) there was a test posting to a new mailing list set up by the OASIS technical committee that is taking forward the OData specification.

To recap, OData is a specification that extends the popular Atom Publishing Protocol (APP) with conventions that make it easy to expose data sources (think relational databases) in a standard way. OData has been driven by Microsoft and is now at version 3, but it seems to be making the transition to a work item at OASIS where it seems likely that a more open specification process will be observed.

I've written about OData before but the best way to play with it is to look at some sample feeds, the Netflix database is one I tend to use for my examples because the data is real and something that is widely understood.

With the work now at a more formal standards body I hope that some of the rough edges of the existing specification can be knocked off. This type of thing is important if OData is to make the transition from a specification which works well if you have client and server libraries from the same vendor to one which can be truly interoperable.

For example, the current specification makes a mess of defining the simple concept of a string-literal parsed from a URL. As a result, it is impossible to make a conforming URI which will get you information about an actor like Peter O'Toole. Here's a URL that a naive user might construct:

http://odata.netflix.com/catalog/People?$filter=Name%20eq%20'Peter%20O'Toole'

Notice that the single-quote character in O'Toole terminates the literal and, sure enough, Netflix returns an error.

Syntax error at position 22.

In fact, there is an undocumented way to get around the problem, using the SQL-convention of doubling the quote character:

http://odata.netflix.com/catalog/People?$filter=Name%20eq%20'Peter%20O''Toole'

I've posted a comment to highlight this issue to the new OData comment list, let's see what happens! It's a public forum so anyone can join though the work of the technical committee itself is behind closed doors (OASIS is a subscription-based membership organization).

I'm a fan of what the basic OData specification is trying to do so getting things like this fixed is important. Just looking at the XML file you get back from the above URI immediately opens up the wonderful world of linked data, giving me relative links like People(69540)/TitlesActedIn from which you can see details of all the films Peter O'Toole has acted in. Don't like XML? Just add ?$format=json to the URL and you can consume the list directly into your web-page.

Last year I gave a lightning talk at a CETIS event in which I encouraged people who were creating REST-based protocols as part of their technical standards development process to have a really close look at OData. Building new specifications using existing protocols can dramatically save time when drafting and make it much easier for people to implement afterwards. And even if OData is not for you, if your application is a good fit for a REST-based approach why not just use APP as it is? Forgot the additional complications of things like WADL, you don't need them. What's more, if you use APP then you can take advantage of existing implementations in web browsers to provide basic and easy to consume views of your data.