[Mondrian] Mondrian 4.0 and regression tests

Julian Hyde jhyde at pentaho.com
Fri Jul 23 20:24:57 EDT 2010

I am currently working on mondrian-4.0 and am reworking a lot of mondrian's
internals, particularly in how schemas are loaded and validated, and in the
mapping of levels and measures onto star schemas.
Usually when I am changing mondrian, if I see a piece of logic in the code,
I will try to preserve that logic, and will rework it if necessary when
internal APIs change. But I don't propose to do that for mondrian-4.0: the
changes to the code are quite widespread, and besides, it's chance to clean
out some of the cruft that has built up over the years.
So... If you have contributed a feature or bug fix to mondrian over the past
years or months, make sure that there is a test case checked in as part of
mondrian's regression test suite. I will do my best to make sure that the
test case stays working, even if the code underneath is all different.
In mondrian-4.0 there will be changes to how schemas are structured. A few

1.	Virtual cubes will be obsolete, or more precisely, any cube can have
multiple groups of measures, each group based on a separate fact table.
2.	Linkages between snowflake tables, currently specified using the
<Join> element, will be specified using new <PhysicalSchema> element that
declares table usages, relationships, and derived columns for the whole
3.	The present XML grammar isn't very forgiving if you get things in
the wrong order: if you define a <NamedSet> before your <CalculatedMember>s
in a cube, mondrian currently ignores all calculated members. The new XML
grammar will be more forgiving.

I recently decided that the XML grammar is sufficiently different that I
would create a new XML grammar. But I promised that mondrian would be
backwards compatible, and I will stand by that. There will be a converter
that will recognize an old-style schema, convert it to a new-style schema in
memory, and then proceed to load the new-style schema. So, old-style schemas
should continue to work. Mondrian-4.0
In a few weeks I will be ready to release the specification for the
new-style schemas. I would appreciate review of the new schemas. Since it is
a major change, mondrian-4.0 will have a long beta phase. During which time
I could use your help testing both new features and backwards compatibility.
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