Sunday, September 16, 2007

Open standards and open-source: The ballad of BIRT and olap4j

This week, I criticized the Eclipse BIRT project for choosing JOLAP as the API between their Dynamic Crosstab support and their cubing engine. I believe that an open-source project should be judged by the extent of its adoption by the community -- after all, if a project fails to serve its community, the community will simply go elsewhere -- and so I hesitate to criticize a project which is clearly pleasing its community.

My argument hinges on the particular importance of open standards for open-source projects, and what I believe is the obligation of an open-source project to embrace standards.

Open standards, open-source

I am not the first person to observe that open standards help open-source projects succeed. An open-source project is likely to find a ready market if it is a better, cheaper, plug-in replacement for an existing software module, and if there is a standard, the boundaries of that module are already well-defined.

But open standards are almost invariably created by commercial software vendors. The open-source community is beholden to these vendors, and the vendors are often in no particular hurry to create open standards.

Barriers to open standards

In public, vendors claim to love open standards as if they were virtues comparable with apple pie and motherhood; in private, they fight them tooth and nail. A couple of years ago, a software vendor asked me to create an MDX interface to their product using mondrian, to satisfy the growing number of their customers who wanted MDX. In private, they admitted that MDX was a good idea, and they would move to it if the majority of their customers demanded it, while in public they derided MDX as inferior to their API. They vendor knew that there is a tipping point when a market moves to an open-standard, and wanted to delay that tipping point as long as possible.

Sadly, this thinking is not confined to commercial software. In commercial and open-source software alike, if a software vendor/project is in a dominant market position, they can choose to ignore open standards. If they deliver a collection of software components connected by proprietary interfaces, customers have to take all or nothing.

Open-source projects build in functionality for which they could have used an open standard API. There are some legitimate reasons for this. Sometimes license balkanization can be blamed, and it would be legally impossible to distribute the two components under the same license; sometimes an open standard exists, but there is no suitable open-source implementation of that standard. But all too commonly, open-source developers fall victim to not-invented-here syndrome, and build a technology where a good open-source alternative exists.

The pressures are particularly intense when the open-source project is backed by a commercial organization, as is the case with Eclipse BIRT. (BIRT is run by Actuate Corporation, a commercial BI vendor, and all of its leaders and key developers work for that company.) The designers naturally want to provide a coherent experience for their end-users, but there is also a temptation to create an architecture which excludes technology of the parent organization's competitors.

I am proud of the efforts we have made to embrace standards in the Pentaho BI Suite, of which mondrian is a part. Among the standards used in the Pentaho suite are CWM, XForm, XPDL, XSLT, XPath, SVG, and XUL, as well as all the standards implicit in the Java and J2EE environments, such as JDBC and JNDI.

Pentaho CTO James Dixon has pointed out that open-source is about more than giving your source code away for free: it requires a process which is transparent (allowing others to know where the project is going) and open (allowing others to participate). Such a process encourages re-use of and contribution to other projects, and in-house projects are ruthlessly 'right-sized' into the smallest module which can be self-contained and sustain its own community. Dependencies between projects are minimized, to make them usable by the largest possible audience. This is a true open-source culture, and it naturally embraces open standards.

A new open standard: olap4j

So it is saddening that there is no API for Java-based OLAP. The only effective OLAP standards are OLE DB for OLAP (fine if you're running Windows) and XML for Analysis (fine if you're prepared to write a program to handle reams of XML). Java developers were promised JSR-069, also known as JOLAP, but the vendors involved (principally IBM, Oracle and Hyperion) failed to agree on a final version. No server vendor released an implementation of the API, and no client tool was released which used it. After it became apparent that JOLAP was truly dead, I removed mondrian's JOLAP interface; mondrian-2.2 was the last release with JOLAP support.

As I noted above, standards are traditionally created by commercial vendors, yet in the case of Java-based OLAP, the vendors have singularly failed to create a standard. The need for an interoperable OLAP client still exists, so I believe it now falls to the open-source community to create one.

Last year, I proposed creating an API called olap4j, and since then, there has been an initial draft of the specification, and work is under way for drivers for both mondrian and for generic XMLA servers.

olap4j and BIRT

As an important part of the open-source BI movement, I naturally tried to include Eclipse BIRT in the olap4j process. Unfortunately the spirit of openness and transparency seems to be lacking in the BIRT project. I have made several attempts, privately and publicly, to engage with BIRT leaders and start collaboration between our projects. They have not responded to my requests, and I can only speculate why that might be. There must be a temptation to create a single BI suite, all parts of which are supplied by Actuate (albeit under an open-source license) rather than present an architecture based on open standards where the users have a genuine choice of components.

olap4j would be a superior API for BIRT to use in order to access dimensional data. JOLAP is dead: it never became finalized as a specification, and there has been no further development, releases of the specification, or implementations since the specification stalled in 2004. olap4j has an active community, interoperates with XMLA, and has multiple implementations available or under development.

The benefit to BIRT's community would be considerable. They would be able to use BIRT's facilities for designing reports, acknowledged as among the best in open-source BI, and run them against the OLAP server of their choice. This would allow reporting users to choose the best OLAP server for their performance requirements and data volumes. Users who already own an OLAP server could use BIRT as an alternative interface to the reporting stack provided by their OLAP vendor.

BIRT could even continue to develop a cubing engine. If successful, that engine could be used as an alternative to mondrian or XMLA by olap4j clients.


I am not optimistic that we will see a change of heart from BIRT, but I wanted to lay things out as I see them.

If you are a member of the open-source BI community -- whether you use Eclipse, Pentaho or just mondrian -- please let the BIRT team know that their decision is making BIRT less open, delivering less value to BIRT's users, and will damage the open-source BI for everyone.


Scott Rosenbaum said...


We have submitted Mondrian to the Eclipse IP process. This can be a fairly long process, but I thought you might be interested that the first step towards progress has been taken.

Your assistance guiding Mondrian through the Eclipse IP process would certainly be appreciated. You can follow or assist at:

Scott Rosenbaum

Anonymous said...

Hello Julian,

I read your post one year later after searching google. BIRT developers took a bad decision using JOLAP instead Olap4j but anyway olap4j seems now as dead as JOLAP.


Luc Boudreau said...

@anonymous: For the record, Olap4j is alive and well.

It's funny you posted that comment on October 25 of this year and didn't notice there has been many releases and much talk on the forums as well as much work being done on the SVN and trackers.

Hey, we're even nearing the 1.0 release; is this dead?

Basarat said...

I would just like to thank you very much for using MDX and creating its implementation. It makes mondrian highly commercially attractive.

Julian Hyde said...


Very glad you like it. And thanks for taking the trouble to say so.