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388 17 Answers to Selected Exercises

for $citation in document("pubmed.xml")//MedlineCitation

where exists

(for $heading in $citation//MeshHeading

where $heading/DescriptorName/@MajorTopicYN="Y"

and $heading/DescriptorName="Glutethimide"

and $heading/QualifierName="therapeutic use"

return $heading)

return $citation

ANSWER TO

EXERCISE8.5

To solve this exercise, extract all pairs of interviews for the same subject such

that the second interview is more than 2 years later, and the BMI attribute is

morethan4.5larger.

for $i in document("healthstudy.xml")//Interview,

$j in document("healthstudy.xml")//Interview

where $i/@SID = $j/@SID

and $j/@BMI - $i/@BMI > 4.5

and $j/@Date - $i/@Date < "P2Y"

return $i/@SID

This query can return the same subject identifier more than once when a

ANSWER TO subject satisfies the criteria multiple times.

EXERCISE8.6

The number of associations is specified by then_associationsattribute of

thego:termelement. The term number is specified by thego:accession

element. The GO namespace must be declared prior to using it in the query.

declare namespace

go="http://www.geneontology.org/dtds/go.dtd#";

document("go.xml")

//go:term[go:accession="GO:0003673"]/@n_associations

Unfortunately, the GO is a very large ontology. When the associations are

included, the GO is a 500 megabyte file. A query such as the one above

would have to read the entire file, which can take a long time. More efficient

techniques for querying such a large ontology were discussed in section 6.3.

ANSWER TO

EXERCISE11.1

Here is one possible solution: