Today we launched version 1.0 of olap4j, the open standard API for accessing analytic databases.
It’s worth mentioning that version 1.0 is a big deal for an open source project. The tag implies maturity and stability, both of which are true for olap4j. The project is over 4 years old, has two robust driver implementations, and many applications in production.
The olap4j driver for Mondrian has been the official way to access Mondrian since version 3.0, and the olap4j driver for XML/A allows access to many XML/A-compliant analytic engines, including Microsoft SQL Server Analysis Services, Mondrian, Palo, and SAP BW.
olap4j was created to address the lack of an open standard API for Java access to OLAP servers. Microsoft had created APIs for the Windows platform (OLE DB for OLAP, and later ADOMD.NET) and for web services (XML for Analysis) and in due course other vendors adopted those APIs as standards, but on Java, the main platform for enterprise applications, you were always tied to the API provided by your OLAP server vendor.
There had been previous attempts to create Java APIs for OLAP, but they foundered because the main vendors could not – or would not – overcome the technical differences between their products. Since OLAP is concerned with constructing dynamic queries to assist an end-user in interactively exploring a data set, most vendors constructed queries using a complex proprietary API to “build” a query using a sequence of transforms.
Relational database APIs such as ODBC and JDBC take a different approach: the query is a string in the SQL language. This allowed the APIs to be simpler, because the semantics of the query language need to be understood by the SQL parser and validator on the server, not by the API itself. And it has allowed the query language to be standardized without affecting the API too much. But the OLAP vendors maintained that such a simplifying approach could not be applied to OLAP.
Microsoft started to prove them wrong when in 1998 they launched SQL Server OLAP Services, the OLE DB for OLAP API, and the MDX query language. This was the first time (to my knowledge) that an OLAP vendor had built its API around a query language as opposed to a set of transforms. MDX played a major role in the success of XML/A: a web services API would have been much harder to use if the queries had built using an object model. Other vendors started to adopt OLE DB for OLAP and XML/A, leaving a void on the one platform Microsoft had no interest in: Java.
Those of us in the open source world felt that void most acutely. Open source projects are organized into discrete components, each talking a standard API, and able to replace a proprietary component by being better, cheaper, faster. If there are no standard APIs, the product stacks sprawl across many components, from client-side to server-side, all made by the same vendor; there is nowhere for open source to get a foothold, and the customer has no choice but to accept the whole hog sold by the vendor.
To redress this, I decided to create a new API. The software would be developed as an open source project, but perhaps more importantly, the specification would be created using an open standards process. As a result, the participants in olap4j read as a who’s who of open source BI. Barry Klawans, then chief architect of JasperSoft, co-authored the original draft; Pentaho’s chief geek, James Dixon, authored the query model; Luc Boudreau, first with the University of Montreal, then with SQL Power, and now at Pentaho, is the XMLA driver’s most active committer and co-leads the project; Paul Stoellberger and Tom Barber have proven and showcased olap4j by developing the first graphical client, Saiku. Paul has also got the XMLA driver working against SAP BW. And we’ve worked closely with Palo developers: Michael Raue worked with us on the spec, and Vladislav Malicevic has gotten the XMLA driver working against Palo.
I knew that to be successful, olap4j needed to be simple and familiar, so I mandated that it would be an extension to JDBC and would use MDX as its query language. The other participants in the specification process took it from there.
Because olap4j is an extension to JDBC, any developer who has accessed databases from Java can easily pick it up. And it can leverage standard JDBC services such as connection pools and driver managers.
Microsoft had proven that an API could be built around the MDX language; there were differences between servers, but these would be mostly in the dialect of MDX supported; just about any server could support the basic metamodel of catalogs, cubes, dimensions, and measures. Some clients would want to build their own queries, and parse existing MDX queries; for these, we added a query model and an MDX parser to olap4j. Use of the query model and MDX parser is optional: if you have an MDX query string, you can just execute it.
We have recently added more advanced features such as scenarios (write-back) and notifications. These features are still experimental (unlike the rest of the API, they may change post-1.0) and are optional for any olap4j provider. But we hope to see more providers implementing them, and clients making use of them. And we hope to see more features added to olap4j in future versions.
The goal of olap4j was to foster development of analytic clients, servers, and integrated analytic apps by providing an open standard for connectivity. That goal has been realized. There is a native driver for mondrian and an XMLA driver that works against Microsoft SQL Server Analysis Services, SAP BW, Jedox Palo. There are several clients, both open and closed source: several components in Pentaho’s own suite, the Community Dashboard Framework (CDF), Saiku, ADANS, SQL Power Wabit, and more.
People are using olap4j in ways that I couldn’t imagine when I started the project four years ago. That’s the exciting thing about an open source project becomes successful and starts to gain momentum: you can expect the unexpected.
Thank you to everyone who helped us get to this milestone.
Visit www.olap4j.org, and download the release 1.0 of the specification and the software.