Friday, November 05, 2004

This is my second day of really brief notes.

According to AN I should have been able to take the exclude code from the old code base, and copy it into the correct position in the new. To do this I started searching for the appropriate code in both code bases. It took some time to confirm, but I eventually concluded that this was not possible.

I also got to see the full extent of the differences between constraint resolution in the old code base and the retro-version in the new (the newer version of this code is in the old code base). This made it very clear that we need to port the constraint resolution code into the new system as soon as possible. There are several reasons for this. The most important is that a new constraint type changes a lot of code with if statements in the new code base, but only needs new classes in the older code base (older system, but newer code). This makes the older system more modular and easier to understand and modify. We will want these changes made quickly, before much more work is done on the new code base, making the changes harder to do (a situation we found ourselves in when trying to move everything over to the current new resolver code base).

In terms of the "exclude" code, I've worked out where the changes need to be. In the old codebase it was wrapped around a normal constraint, and inverted the results as they came back. The new architecture does not allow for this. The best example of this is shown with a remote resolver. It is impossible to return all data except the result of a constraint because the only data available is that result. There is no way to get the rest of the data from the server (without constructing another query).

So each resolver will need to handle an "inverted" constraint and return the correct answers. For our purposes, we only need to be capable of doing this on the StatementStoreResolver to get our old functionality. However, in future we may need to consider mandating that all resolvers be capable of handling an inverted resolver.

In the meantime, the StatementStoreResolver code needs a new Resolution object (basically a Tuples) which can return all data except that which a constraint resolves to. This won't be too hard, but will take a little while to code.

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