Microsoft are deprecating Native XML Web Services in SQL Server 2008, and if I understand the productmanagerese correctly, that means that they are abandoning XML for Analysis (XML/A) as an interface to Microsoft Analysis Services.
(I may be mistaken. Can someone who is closer to Microsoft's roadmap clarify how OLAP applications on non-Windows systems are supposed to access Microsoft Analysis Services?)
UPDATE, 2010/6/18 09:50 PDT: It turns out that I am mistaken, and I received several comments pointing this out. The real story is that Microsoft is deprecating native XML access to SQL Server (the relational database, not the OLAP server). I have left the rest of the blog post as I originally wrote it, but please read it in the light of the new evidence.
But if true, that would be a worrying development for those of us who want to build interoperable OLAP applications. (In particular, those with clients on non-Windows platforms such as Linux.)
It's funny; Microsoft was the leading company pushing web services back in 2000. Everyone thought that it was too verbose a protocol for passing large data sets around, but Microsoft had a big problem to solve — its aging DCOM infrastructure — and pushed it through.
I was at a meeting in Redmond (in 1999, if memory serves) when Microsoft launched XMLA. The SQL Server OLAP Services team demoed the interoperability by showing a Java program running on Solaris (or possibly Linux... my memory is fading...) connecting to a Microsoft OLAP Services server. They joked that they could have been fired for having a non-Windows machine in the building. But nevertheless they made their point: XMLA was interoperable, and that was unprecedented among OLAP applications at the time.
Soon afterwards Microsoft started using compressed XML for its XMLA calls and responses, thereby reducing the problem. Unfortunately their compression technology was proprietary, so the rest of us had to carry on using uncompressed SOAP calls. It gave Microsoft's drivers an unfair advantage over other drivers attempting to talk to Analysis Services.
It's ironic that Microsoft should abandon a standard that they created, and which has been astoundingly successful. I suspect that they have gotten tired of maintaining it when their own drivers use more efficient, proprietary wire protocols.
If Microsoft is deprecating XMLA, I doubt that it will disappear for some years to come, but it is bound to be a concern for people building applications now that they intend to be running for several years.
Of course, one thing people can do to insulate themselves from the future is to build their OLAP applications in Java using olap4j. Whatever net protocol Microsoft adopts to replace XMLA, we will keep the olap4j driver for Analysis Services working, so you shouldn't need to change your application.