"DQL"

	DQL
	A Query-Answering Language for DAML+OIL

Roles For Reasoning In The Semantic Web

	Ontology developers
		Classification
		Inconsistency detection
		Evolution
			Debugging and refinement
		Maintenance
		Integration
	Web site developers
		Recognition
		Inconsistency detection
		Evolution
			Debugging and refinement
	For users seeking services
		Service composition
			Planning
		Execution monitoring
	For users seeking information
		Query-answering

A DAML+OIL Reasoning Working Group

	Promote interaction and collaboration among DAML contractors working on reasoning
		E-mail distribution list
		Web site
	Design consensus DAML query language?
		Design a consensus language for querying DAML+OIL knowledge bases
	Design consensus DAML justification language?
		Do this in conjunction with and after design of DAML rule language.

Objectives for DQL

	Standard for querying DAML+OIL KBs
		Language for:
			Queries
			Answers to queries
			Justifications for answers
		Protocol for:
			Agent-agent interaction during query-answering
	Support development of:
		DAML+OIL query-answering reasoning methods
		Interoperating DAML+OIL query-answering agents
	Provide basis for Semantic Web standard
		For full DAML and OWL languages

DQL Design Issues

	The formal properties of queries and answers
		What is a query?
		What is an answer and what does it mean?
	Inferring answers may be expensive
		Impractical to always try to compute all answers
	Answers may only be known to exist
	Equivalence of multiple answers
	There may be an infinite number of answers
	Is a query to a specific knowledge base?
	Justifications for answers
		What are they and when should they be computed?
	Are queries and answers represented in DAML+OIL?

What is a DQL Query?

	A DML query necessarily includes:
		Pattern – collection of DAML+OIL sentences in which literals and/or resources have been replaced by variables
			E.g. (owns ?p ?c)  (type ?c Car)  (color ?c Red)
				“Who owns a red car?”
		Distinguished Variables in the pattern whose bindings are sought
			E.g., {?p}

What is a DQL Query?

	A DML query necessarily includes:
		Pattern
		Distinguished Variables
	A DML query optionally includes:
		DAML+OIL knowledge base with respect to which the query is posed
			All queries are answered with respect to a knowledge base
			The answering agent may select the knowledge base
		…

What is a DQL Query?

	A DML query necessarily includes:
		Pattern
		Distinguished Variables
	A DML query optionally includes:
		DAML+OIL knowledge base
		Premise – additional DAML+OIL sentences to facilitate if-then queries
			E.g., “If C1 is a Seafood Course and W1 is a drink of C1, what color is W1?”
			Premise: (type C1 Seafood-Course)  (drink C1 W1)
			Pattern:  (color W1 ?x)
		Justification request

What is a DQL Answer?

	A DQL answer necessarily contains:
		Bindings for some or all of the distinguished variables
			E.g., “Who is a parent of who?”
			Pattern:  (parent-Of ?p ?c)
			Distinguished variables:  {?p ?c}
			Bindings:  {(?p Earl)  (?c Richard)}
			or if the child is not known:  {(?p Earl)}
			The sentences produced by applying the bindings to the pattern and treating the remaining variables as existentially quantified are entailed by the KB
				E.g., (exists  ?c  (parent-Of Earl ?c))
			The bindings include all the bindings for distinguished variables that the answering agent has
				A conformance requirement

What is a DQL Answer?

	A DQL answer necessarily contains:
		Bindings for some or all of the distinguished variables
			The sentences produced by applying the bindings to the pattern and treating the remaining variables as existentially quantified are entailed by the KB
			The bindings include all the bindings for distinguished variables that the answering agent has
			Each binding is to a literal or URI in the vocabulary of the KB
				Not allowed:
					Arbitrary term expressions (descriptions)
					E.g., { … (?c “A Person all of whose uncles are lawyers”)}
					Skolem constants

What is a DQL Answer?

	A DQL answer necessarily contains:
		Bindings for some or all of the query pattern’s distinguished variables
		Query to which this is an answer
		Answering Agent that produced the answer
		Knowledge base used to answer the query
	A DQL answer optionally contains:
		Justification if requested

DQL Queries

	DQL is for answering queries of two forms
		When there are distinguished variables:
			“What resources or literals from the KB’s vocabulary denote objects that make the query pattern true?”
				E.g., “Who are the parents of Richard?”
		When where are no distinguished variables
			“Is the query pattern true in the query KB?”
				E.g., “Does Earl have any children?”

How Many Answers?

	Answers are generated one at a time
		Response to a query is one of the following:
			Answer and Continuation – The continuation can be used to request a next answer from the answering agent
			“no” – no further answers are entailed by the KB
			“unknown” – no further answers can be produced by the answering agent (but more may be entailed)
		Every answer contains a distinct set of bindings
			But two sets of bindings may denote the same objects
	More capabilities can be built using continuations
		E.g., 4Find all answers
		4Each answer denotes a distinct set of objects

Example Query-Answering Dialogue

	“child” is an inverse of “parent”
	Every “Person” has 2 “parent”s
	Every “parent” of every “Person” is a “Person”

DQL Design Issues

	The formal properties of queries and answers
		What is a query?
		What is an answer and what does it mean?
	Inferring answers may be expensive
	Answers may only be known to exist
	Equivalence of multiple answers
	There may be an infinite number of answers
	Is a query to a specific knowledge base?
	Justifications for answers
		E.g., proofs, premises, sources, certifications, etc.
		Not yet designed
	Are queries and answers represented in DAML+OIL?
		Yes, using a DAML-Q ontology(?)

Feedback Welcome

	Birds of a feather session on Thursday
		11:00 to noon
	During this meeting, talk with Pat & myself
	Ongoing, send e-mail to the joint committee