Re: DQL Description (for today's telecon)

From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 02/11/02 

I have several comments on the DQL informal description.

First, I would much prefer to have a definition of what querying is
supposed to be separated from all the interface ``fluff''.

Second, the informal description has a problem with equality.

I would thus prefer something like

QUERYING

* Knowledge Base - A Knowledge Base is ....  (I'm actually not sure what to
  put here.)

* Query Pattern - A Query Pattern is

* Querying Binding - A Query Binding for a query pattern is a partial map
  from the distinguished variables of a query pattern to (singleton sets
  of) literals or non-empty sets of URIs plus fragments (identifiers).

* Bound Query - Given a query pattern and query binding, a bound query is
  the result of replacing each variable in the query pattern that has a map
  in the query binding by an element of the set that is its mapping, and
  adding in pairwise equality statements for all the elements of each of
  the binding sets.

* Answer -  An answer to a query pattern on a knowlege base is a query
  binding for the query pattern such that the knowledge base entails the
  bound query for that query pattern.

* Single Query Binding - A Single Query Binding is a query binding where
  all sets are singletons.

* Query Answer Expansion - The expansion of a query answer is the set of
  single query bindings that map each variable into one of the mappings for
  that variable from the query answer.

* Query Answer Specificity - A query Q1 is more specific than another Q2 if
  Q1 maps all the variables that are mapped by Q2 and the value of each map
  in Q2 is a superset of the corresponding map in Q1.

* Query Answer Containment - A query answer Q is contained in a set of
  query answers S if all the expansions of Q are less specific than some
  element of S.

* Answer Set - An Answer Set for a query pattern on a knowlege base is a
  set of query bindings for the query pattern such that
  1/ each element of the answer set is an answer for the query pattern, and
  2/ any other answers for the query pattern are contained in the answer
  set.


Only then would I go on to define the interface.


The interface itself needs to talk about completeness and fairness.


peter

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