09: SPARQL Advanced

Question 1

XML schema are ____ format, whereas DF, RDFS, and OWL are about ____ ____.

Answer 1

XML schema are message** format, whereas DF, RDFS, and OWL are about **knowledge** **representation.

Question 2

Many RDF ____ ____ hold multiple ____ ____ and record information about each ____, allowing an application to make ____ that involve information from more than one ____.

Answer 2

Many RDF data stores** hold multiple **RDF** **graphs and record information about each graph, allowing an application to make queries that involve information from more than one graph.

Question 3

A SPARQL query is executed against an ____ ____ which represents a ____ ____ ____.

Answer 3

A SPARQL query is executed against an RDF** **dataset** which represents a **collection** **of graphs.

Question 4

A constraint, expressed by the keyword FILTER, is a ____ ____ ____ over the whole group in which the filter appears.

Answer 4

A constraint, expressed by the keyword FILTER, is a restriction** **on** **solutions over the whole group in which the filter appears.

Question 5

Group Graph Patterns

Answer 5

• a group graph pattern is delimited with braces {}

Question 6

Multiple Optional Patterns

Answer 6

• graph patterns are defined recursively
• a graph pattern may have zero or more optional graph patterns, and any part of a query pattern may have an optional part

Question 7

Query patterns can involve both the ____ ____ and the ____ ____.

Answer 7

Query patterns can involve both the default graph and the named graphs.

Question 8

What is the query to list the name of all graphs?

Answer 8

SELECT DISTINCT ?g {graph ?g {[] [] [].}}

Question 9

Change the following SELECT command so that as well as writing the name of graphs (datasets), it writes the number of triplets in each graph as well.

SELECT ?g count(?g)

{graph ?g {[] [] [].}}

Answer 9

SELECT ?g count(?g)

{graph ?g {[] [] [].}}

GROUP BY ?g

Question 10

When working with subqueries in SPARQL, in nested queries there is a scheme called ____ ____ ____ ____.

Answer 10

When working with subqueries in SPARQL, in nested queries there is a scheme called innermost** **first** **processing** **scheme.

Question 11

What is the output of the following?

Answer 11

Question 12

Federated Query

Answer 12

• the ability to take a query and provide solutions based on information from many different sources

Question 13

Top-to-Bottom Order Approach

(Federated Queries)

Answer 13

• if a variable is bound above the invocation of the remote source then it is passed as a parameter
  
  • would instead be better if the federated subquery would leave all latitude to the implementation to decide join order and would thus be more in the non-procedural spirit of SPARQL

Question 14

Ideally, federating queries should be ____.

(And what is the drawback of this?)

Answer 14

Ideally, federating queries should be transparent.

• comes at a cost with SPARQL: multiple end points in principle can match any of the triple patterns in a query

Question 15

SERVICE keyword

Answer 15

• instructs a federated query processor to invoke a portion of a SPARQL query against a remote SPARQL endpoint

Question 16

DL (Descriptive Logic)

Answer 16

• family of knowledge representation languages on which OWL is based
• allows humans and computers to exchange well-structured ontologies
• facilitates logical deduction to infer additional knowledge, a process referred to as reasoning
• balances expressivity vs complexity of reasoning

Question 17

What two important issues can DL reasoners help reveal?

Answer 17

• inconsistencies & misclassifications
• hidden dependencies

Question 18

Main Characteristics of DL

Answer 18

• modes the binary relationships among the entities of certain domains
• can use knowledge in ontology to infer further facts about individuals
• can form statements linking concepts and roles (by existential and universal restrictions)

Question 19

What 3 elements is DL involved with?

Answer 19

• individuals/constants (e.g. David)
• concepts/unary relations (e.g. Person)
• roles/binary relations (e.g. isMarried)

Question 20

TBox

Answer 20

• defines the ontology that serves as conceptual view over the data in the ABox terminology

Question 21

ABox

Answer 21

• set of assertions that
  
  • state membership of individuals to concepts
    
    • C(a)
  • and role membership for pairs
    
    • R(a,b)

Question 22

State the following statement in DL as well as in Protege:

Assume that for a person to be called a student, he/she needs to attend at least 4 courses.

Answer 22