Wednesday, February 3, 2010

CM 1.0 Simple Query Syntax, how we got here

Often I get asked about what how it was decided what was included into the CM 1.0 Simple Query Syntax, so I figured I'd take a couple of minutes to summarize some key points. The goals for the 1.0 were quite simple: produce a simple syntax that supports our scenarios and that will work with SQL and SPARQL based back-ends. One of the most obvious omissions from the query syntax is the "or " operator, or UNION if you are from SPARQL. This was intentional since the CM WG realized that all scenarios could be accomplished by having support for the "in" operator. By doing this, we avoided the complexity of having to support grouping of terms with parenthesis.

The type of query we saw as being key to support in 1.0 were queries such as: Show me all open change requests assigned to a specific user
?oslc_cm.query= owner="bob" and status in ["submitted","working"]

Beyond that, most other operators are quite common. Another primary scenario was the ability to retrieve a set of change requests that have been modified since a given date. Which is supported by both having the Dublin Core usage of dc:modified and comparison operators such as:

This has been proven to be very powerful and easy to map to service provider search capabilities. At some point there may need to be support for a full query syntax service, which could be a unique URL end point to post a query to. We'll have to wait and see how this plays out over time.

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