10 XML Retrieval

Question 1

Structured retrieval

Answer 1

Search over structured documents

Question 2

XML

Answer 2

Extensible markup language. A standard for encoding structured docu- ments. Most widely used standard.

Question 3

XML element

Answer 3

A node in a tree

Question 4

XML attribute

Answer 4

An element can have one or more XML attributes

Question 5

XML DOM

Answer 5

Document Oject Model. The standard way for accessing and processing XML docs. The DOM represents elements, attributes, and text within elements as nodes in a tree. With a DOM API, we can process a XML document by starting at the root element and then descending down the tree from partens to children.

Question 6

XML Context/contexts

Answer 6

An XML path.

Question 7

Schema

Answer 7

A schema puts constraints on the structure of allowable XML documents for a particular application. A shcema for ShakespearÕs plays may stipulate that scenes can only occur as children of acts and that only acts and scenes have the number attribute.

Question 8

NEXI

Answer 8

A common format of a XML query.

Question 9

Structured document retrieval principle

Answer 9

The principle is as follows: A system should always retrieve the most specific part of a document answering the query.

Question 10

Indexing unit

Answer 10

Which parts of a document to index.

Question 11

Schema heterogeneity/diversity

Answer 11

In many cases, several different XML schemas occur in a collection because the XML documents in an IR application often come from more than one source. This is called schema heterogeneity. It presents yet another challenge(s):

1. Comparable elements may have different names like author vs creator.
2. The strucutral orginization of the scemas may be different: Author names are direct descendats of the node autor, but in a different struc- trure there can be firstname and lastname as dicrect children from author.

Question 12

Extended query

Answer 12

We can support the user by interpreting all partent-child relationships in queries as descendant relationships with any number of intervening nodes allowd. These are extended queries.

Question 13

Structural term

Answer 13

To index all paths that end in a single vocabulary term, in other words, all XML-context/term pairs. We call such an XML-context/term pair a structural term.

Question 14

Text-centric XML

Answer 14

Where we match the text of the query with the text of the XML docuemnts 31

Question 15

Data-centric XML

Answer 15

Mainly encodes numerical and nontext attribute-value data. When quering data-centric XML, we want to impose exact match conditions in most cases. A query can be: ÒFind emplyees whose salary is the same this month as it was 12 months ago.Ó This query requires no ranking. It is purely strucutral and an exact matching of the salaries in the two time periods is probably sufficient to meet the users information need.