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Google Search Appliance .NET solution

I recently worked on a project to integrate the search results from a Google Search Appliance into a .NET application. Although it seems like a pretty straight forward task, there were some small issues that I thought I might share.

The communication with the Google Search Appliance is made simply with a HTTP GET request, which returns an XML formatted response. As for the Suggest service, the request looks about the same but the result returned is JSON encoded. For more information, please see the Google Search Appliance documentation, which is very extensive.

Since this solution was to incorporate several languages, the .NET application had to support and differentiate the languages. The GSA has very good built-in language support but there were at least one thing that was not completely obvious.

The GSA uses either HTTP headers or query string parameters to determine in which language the request is made. If neither of these are supplied the GSA may not return a correct response. This was the issue in our case, where we got unpredictable results in the spelling suggestions.

Summary: Always send an appropriate Accept-Charset and Accept-Language HTTP header.

XPath or LINQ to Xml?
There is already a publicly available .NET library (GSALib) to communicate with the Google Search Appliance, but for several reasons I chose not to use that library and build our own customized library. Since all responses from the GSA is XML formatted a key element in the communication is the XML parsing.

In .NET today there are basically two different choices, XPath or LINQ to XML. In the decision making process there were two key features to consider, ease of use and performance. MSDN published an article on this subject, Comparison of XPath and LINQ to XML. The following blog even took their time to make a little performance test, XPath vs LINQ to XML.

Summary: I chose LINQ to XML mostly because of its composition, which produces code that is easier to read and modify since we practically always read all elements in the XML file.


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