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XML and XML in DLESE

Katy Ginger

November 2003

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XML Purpose

Provide a container for data that is presentation and platform independent

Container for data that is flexible and extensible; user defines the tags and content

A single container for data that has multiple purposes and uses in a variety of software or web applications

Note: XML databases exist now

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What is XML data?

Is called instance documents Consists of user defined tags Is well-formed and valid The content that can be defined and controlled

See DLESE Annotation Metadata Record example

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Built-in Primitive Types

Strings: e.g. strings Binary: e.g. boolean Numeric: e.g. decimal, float, double from

which integer is derived Date/time: e.g. date, dateTime, duration, time

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Well-formed and valid XML

Correct

<car>

<make>Dodge</make>

<model>Spirit</model>

<year>1994</year>

<owner>

<name>you</name>

<plate>CO</plate>

</owner>

</car>

Incorrect

<car>

<make>Dodge</make>

<model>Spirit</model>

<year>1994

<owner>

<plate>CO</plate>

<name>you</name>

</car>

</owner>

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DTD, Schemas & Namespaces

DTD: Document Type Definition

Describe the elements of XML instance documents

Not well-formed XML Some data-typing Namespaces harder to

deal with

Schemas Describe the elements of

XML instance documents Well-formed XML Strong data-typing Namespaces are easier to

deal with

Namespace:

Collection of related element names identified by a name label (e.g. dc:title where dc is for Dublin Core)

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XML Schema Design Philosophy

Decide where to apply XML, it’s good for:– Data archiving– Message passing– Presentation documents

Decide between global & local XML declarations– Russian Doll Design– Salami Slice Design– Venetian Blind Model

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Russian Doll Design

Schema mirrors structure of the instance doc Elements are declared inside parent elements All elements are local in scope Elements may appear multiple times but can’t be

referenced elsewhere Changes on an element affect only the content model

(parent element) of the element being changed Hides namespace complexities

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Salami Slice Design

Each element/attribute is declared globally Content models are then pieced together

through references Elements can be used anywhere and in

multiple schemas Changes on an element affect it everywhere

the element is used Does not hide namespaces

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Venetian Blind Model

Elements/attributes are defined as types (simple or complex)

Content models are made of types Types are reusable and extendable Changes on an element affect its type and

where the type is used Namespaces can be hidden or not hidden

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How to control tag content

Use restriction and enumeration elements Use regular expressions

See DLESE Annotation Metadata Record example

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How DLESE uses XML

DLESE systems act on metadata All DLESE metadata is stored as flat XML files DLESE harvests metadata XML files from other

digital libraries DLESE provides metadata XML files to other

digital libraries DLESE transitioned to schemas in Spring 2003 DLESE schemas use the Venetian Blind Model

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XSLT (Extensible Stylesheet Language Transformation)

Acts on valid and well formed XML documents like instance docs and schemas

Used to create new text, HTML or XML docs DLESE uses it to crosswalk our metadata

format to the Dublin Core metadata format