> lukas I thought that we could enrich the metadescription themselves to
> let us know what are the selectors we can use and the other object we
> can use (such as today lastMonth....)

Exactly, Magritte does not provide this information right now. In
fact trough the history of Magritte there were some attempts in
providing something like that as part of the core framework, but it
hasn't happened yet as it turned out to be a bit difficult to make it
useful in different contexts.

What I did in this project I sent the screenshot was to create a
comparator object that represented a sentences like:

        creation date is earlier than yesterday
        tags contains seaside
        number of visits between 1000 and 2000
        etc.

As you can observe this is basically a Smalltalk message to a
receiver with some arguments. How to build these messages? I extended
descriptions to return comparators they support: this is basically a
collection of selectors associated with a collection of descriptions
for each of their arguments. Then I build a UI that (1) lets users
choose the description they want to query, (2) displays a drop down
with the selectors (or better a readable label) that let users choose
an operation and then (3) display editors for the arguments based on
the descriptions.

That's the basic strategy. We can do some pair programming next week
and try to come up with something that is useable as part of the
core, if you like?