We have a client that has Oracle Standard, and a project that would be ten times easier addressed using OLAP. However, Oracle only supports OLAP in the Enterprise version.
Migration to enterprise is not possible
I'm thinking of doing some manual simulation of OLAP, creating relational tables to simulate the technology.
Do you know of some other way I could do this? Maybe an open-source tool for OLAP? Any ideas?
I find that it's the schema that causes most of the issues people have with querying a database. OLAP forces you to either a flat table or a Star/snowflake schema which is easy to query and comparably faster to the source oltp tables. So if you ETL your source to a flat table or star schema you should get 80% of what you get from OLAP, the 20% being MDX and analytic functions and performance.
Note that you should get a perf boost with a star schema in relational database as well and Oracle probably has analytic functions in PL/SQL anyways.
You can simulate OLAP functionality using client side tools pointed at a relational database.
Personally I think the best tool for the job is probably Tableau Desktop. This is an amazingly sophisticated front end analytics tool that will make your relational data look multidimensional without much effort, and the tool itself is really mind blowing. They have a free trial so you can take it for a spin. We use Tableau heavily for our own analysis and have been very impressed. Of course, this tool also works with multidimensional databases as well, so if you end up with some cubes at the end of the day you can continue to use the Tableau front end.
As for open source, you could try out Palo - an open source MOLAP server and Excel front end.
If you are interesting in building your own reporting front end and use .NET there are a number of components (such as the DevExpress PivotGrid or the several tools from RadarSoft) that will do the same thing, but will require some elbow grease to get wired together.
Whilst MS SQL Server offers OLAP, you'll need an Enterprise licence to use a cube in a live environment that is web-facing.
Try an open-source OLAP server called 'Mondrian'. IIRC the XMLA API on this is sufficiently compatible with AS to fool Pivot Table Services, which would allow you to use it with ProClarity or Excel.
IIRC it was originally designed to work over Oracle - it is a HOLAP architecture using base tables in the underlying relational store and caching aggregates. You can also make use of materialised views and query rewrite in the underlying Oracle database to do aggregates.
A few more thoughts on this topic:
Actually, Oracle Standard does have an OLAP facility based on a descendent of Express embedded in the database engine and storing its internal data structures in BLOBs in the main tablespaces. Using this is technically possible but not necessarily advisable for the following reasons:
It uses a highly non-standard OLAP query engine with very little third party tool support (AFAIK ArcPlan is the only third-party OLAP front-end supporting 10g+ OLAP), poor documentation for the query language and almost no third party literature describing it. This will work with B.I. Beans if you feel like writing a JSP front-end. It is not compatible with MDX at all. As of early 2006 the best Oracle could do when asked about drillthrough (this functionality was not supported in Discoverer 'Drake') was to recommend building a JSP apllication using B.I. Beans.
The reason that there is no migration path from Standard to Enterprise is that Enterprise is actually what used to be Siebel Analytics. Standard is the old Oracle OLAP/Express descendant which Oracle partners recommended avoiding even before Oracle bought out Seibel. Oracle has not even attempted to support migrating.
From this point of view, Mondrian is actually the most cost-effective OLAP solution for an Oracle Standard Edition shop. You can get a supported version from an outfit called Pentaho[1]. The next cheapest is Analysis Services, which comes with SQL Server. Following that you are into the likes of Hyperion Essbase, which will be an order of magnitude more expensive than SQL Server or any supported verion of Mondrian.
You might want as well to give a try to www.icCube.com - we're quite flexible on the data-source used to populate the cube and are quite cost effective compared to the big actors of the market.