TU Wien:Semistrukturierte Daten VU (Woltran)/Zusammenfassung

Semi-structured data

• SSD can be represented as a labeled tree

XML

• An element consists of:
  • start tag: <element-name>
  • content
    • empty
    • simple content — text
    • element content — one or more elements
    • mixed content — text and elements
  • end tag: </element-name>

Empty elements can be abbreviated as <element-name/>.

• XML is case-sensitive.
• XML predefines five entity references: < & > " '
• <!-- this is a comment -->
• <? this is a processing instruction ?>
• default namespace is declared as xmlns="name"

Document Type Definition (DTD)

A DTD lists all the elements and attributes the document uses. The order of declarations is not significant.

<!ELEMENT person (name, tel, fax, email+)>
<!ELEMENT name (#PCDATA)>
<!ATTLIST person id_number ID #REQUIRED>

If a document matches the schema, it is valid, otherwise, it is invalid. Validation errors may be ignored by applications.

Document Type Declaration:

<!DOCTYPE person SYSTEM "http://www.example.com/dtds/person.dtd">

The location can also be relative.

XML Schema Definition (XSD)

simple elements

Contain only text. We can add restrictions.

Built-in types:

• xsd:boolean, xsd:string, xsd:decimal, xsd:integer, xsd:date, xsd:time, etc.

Restrictions on Values

• xsd:minInclusive
• xsd:maxInclusive
• xsd:minExclusive
• xsd:maxExclusive
• xsd:enumeration
• xsd:pattern (regex)
• xsd:whiteSpace
• xsd:length
• xsd:minLength
• xsd:maxLength

Complex elements

Contain other elements and/or attributes.

Order Indicators

• all
• choice
• sequence

Occurence Indicators

• minOccurs
• maxOCcurs

Keys and References

XPath

13 axes

Extensible Stylesheet Language Transformations (XSLT)

Templates match the input document, and define the output.

Templates for the subtree are only called with

<xsl:apply-templates/>

XSLT has the following default templates:

• for root and elements: apply templates for child elements
• for text elements: copy content to output
• for attributes: copy value to output

Exactly one template is executed, more specific XPaths are prioritized.

XQuery

FLWOR

for ... let ... where ... order by ... return ...

Parsing

• event-based: SAX (Simple API for XML)
• tree-based: DOM (Document Object Model)