OData Client goes Open Source

Microsoft is trying to succeed where web services failed before with their new Open Data Protocol (oData).

A few years ago, I had an epiphany when listening to Don Box talk about data services and web services. Web services and web sites are merely public facades to your internal databases. Web sites expose your database rendered as HTML while web services expose them in some sort of data format, defined on a case-by-case basis.

With Web Services, developers need to define what bits of information should be exposed and how it is exposed (this applies to both SOAP and REST-based services). The problem is that developers might not have the time to spend on exposing every possible bit of interesting information that you maintain in your databases. Most importantly, there are very few web services that provide server-side queries making the information harder to mine.

oData is a little bit different, for a given oData endpoint (like http://odata.netflix.com/Catalog/CatalogTitles) you can request that the server do some work for you, for example, you can pass a query that will limit the results to only those that you are interested in, and you can also specify the information that you are interested in.

For example:

It seems like Microsoft is doing the right things to get oData to be adopted. It reused Atom as the exchange format, made the services REST-based, it made client libraries available for many developer platforms and placed the spec under the OSP.

Consuming oData sources

Microsoft is taking a very Google-y approach with oData. They have created client libraries for a wide range of platforms to encourage adoption of this new way of exposing data.

In addition to the JavaScript, Java, PHP, .NET and Objective-C bindings, Microsoft has announced that they will be open sourcing the .NET client library under the Apache 2 license. I was pleasantly surprised to learn that they were open sourcing this code, as we can consume it right away on Mono.n

So this is good news for everyone that wants to consume the information. The bindings for .NET are in particular great since you get strongly typed client-side code that you can use to invoke remote servers.

Producing oData: the need to open source System.Data.Services

This is trickier, and I believe that if Microsoft wants to bootstrap the oData universe they need to seed this space not only with some existing services but also with an open source OData server implementation for Unix.

I should further add that they should not wait a single minute and open their server-side .NET implementation if they want to accelerate the oData adoption.

Let me explain why.

Although the client libraries are great step to drive the adoption of the protocol for clients, it will do very little to unlock the data that sits today out in the web behind Linux servers running PHP, Java, Ruby or Python-based applications.

At the end of the day, the client side code is a relatively simple parser for an XML file format. The server side on the other hand is much more complicated to get right.

The server side requires a complete implementation of the query syntax, selection as well as access control and transaction support required to expose the data safely.

It is clearly possible to implement the oData server technology, IBM did it for WebSphere, but this is an unnecessary wait. Placing a standard under the OSP and documenting it is not enough to drive open source or even third party implementations.

If Microsoft were to open source their server side implementation of oData, we could overnight allow Linux users to expose their data in a format that can be mined. Linux users would only need to run a Mono front-end to the System.Data.Services library to expose the data that currently lives in their servers and is being served by Joomla, Wordpress, Rails, Django front-ends to become available as data services.

Witness what happened with the M modeling language: great idea, OSP-covered, and yet the steep work required to implement it means that not a single implementation has been created in the 18 months since the project went public.

Update: I stand corrected, Douglas Purdy points out that there is an open source implementation of M built with Javascript here.

Ok, so not the best example, risking another egg in my face, I want to say that chances are that jsmeta is not a complete implementation of M.

More on oData

A detailed overview is available on the oData site.

The best intro to oData that I have seen is Douglas Pourdy tour-de-force during the second day keynote as he walks through all the pieces in a span of 20 minutes.

The MIX sessions on oData are packed with great information. The transaction and access control requirements on the server-side support are discussed on the How to create a feed for that session.

If you want to explore oData services, you can use this Silverlight application to build your queries.

Posted on 22 Mar 2010 by Miguel de Icaza
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