xml for information management

XML for Information Management – Day 4: Logical and Physical Structure of XML DocumentsAiri Salminen

XML for Information Management

University of Erlangen-NurembergComputational Linguistics

Instructor: Professor Airi Salminenhttp://users.jyu.fi/~airi/

12.1.-16.1. 2009


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Day 4: Logical and Physical Structure of XML Documents

1. Components of the logical structure2. XML documents as trees3. Entity types4. Entity declarations and references5. XML processor treatment of entity

references6. Motivations for the use of entities

Outline


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1. Components of the logical structure

• declarations

• elements

• comments

• processing instructions


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document ::= prolog element Misc*

declarationscommentsprocessing instructions

elementscommentsprocessing instructions

commentsprocessing instructions


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‣ XML declaration [23]

‣ document type declaration [28]

‣ markup declaration [29]

• element type declaration [45]

• attribute list declaration [52]

• entity declaration [70]

• notation declaration [82]

‣ encoding declaration [80]

‣ standalone document declaration [32]

‣ text declaration [77]

Declarations:


to constrain the logical structure

to constrain the physical structure


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Typical element type declarations:


mixed content defined

element content defined

<!ELEMENT product (mfg, model, description, clock?)><!ELEMENT model (#PCDATA)><!ELEMENT description (#PCDATA | feature)*><!ELEMENT clock EMPTY>

empty element defined


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empty element defined:

<clock></clock><clock/>

<!ELEMENT clock EMPTY>

two forms of the element allowed in a well-formed document:


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element content: definition by content models with metasymbols

* iteration (none or more)+ iteration (once or more)| alternatives? optional, successive( ) grouping

#PCDATA is not accepted in the content model!

<!ELEMENT table (caption?, (col*|colgroup*), thead?, tfoot?, (tbody+|tr+))>

Example from XHTML 1.0 Strict DTD:


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mixed content: definition has basically two forms

(#PCDATA)(#PCDATA | e1 | … | en)*

<!ELEMENT text (#PCDATA)><!ELEMENT section (#PCDATA | subsection)*><!ELEMENT section (#PCDATA | subsection | paragraph)*>

#PCDATA is always included in the content specification and comes first in the list of alternatives

examples:


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• to define the set of attributes pertaining to a given elemen type

• to establish type constraints for these attributes

• to provide default values for attributes

Attribute list declarations



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attribute name

<!ATTLIST poem author CDATA #REQUIRED >

attribute type: string

constraint: the attribute must be specified for all elements of type poem

element type



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Defining constraints

#REQUIRED: attribute must always be provided in all elements of the given type

#IMPLIED: attribute can be provided in a element; no default value is provided

AttValue: default value is given between single or double quotes

#FIXED AttValue: instances of the attribute must match the given default value

[60] DefaultDecl ::= '#REQUIRED' | '#IMPLIED'| (('#FIXED' S) ? AttValue)



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Attribute types

[54] AttType ::= StringType | TokenizedType | EnumeratedType

• ENTITY, ENTITIES: entity names

• NMTOKEN, NMTOKENS: text tokens consisting of characters accepted in names

• ID: names that uniquely identify elements

• IDREF, IDREFS: references to ID type identifiers

tokenized types:

enumerated types:• NOTATION, NOTATIONS: identify notations• enumeration



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<?xml version=”1.0”?><!DOCTYPE text [<!ELEMENT text (line+)><!ELEMENT line (#PCDATA)><!ATTLIST line

id ID #REQUIREDseeline IDREFS #IMPLIED> ]>

<text><line id=”r1”>This is the first line</line><line id=”r2” seeline=”r1”>This is the second line, but look at the first too</line></text>



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2. XML documents as trees

<Chapter section = '1' ><Narration narrator='Benjy'><Imagery place='tree' mode=simile sense='smell'><Fragment code='1.12'><Paragraph id='143'><Subject person='Caddy'>She</Subject>smelled like trees.</Paragraph></Fragment></Imagery></Narration></Chapter>

XML-aware web browsers support the visualization of the hierarchic structure: example


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XML specification defines a concrete syntax for XML documents.

W3C has defined four slightly different abstract models to decribe the abstract syntax of XML documents:

• XML Information Set• DOM model• XPath 1.0 model• XQuery 1.0 and XPath 2.0 data model

Analysis of differences in the models: Salminen, A., & Tompa, F.W. (2001). Requirements for XML document database systems. Proc. of the ACM Symposium on Document Engineering (DocEng '01) (pp. 85-94). New York: ACM Press.

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<poem author = ”Murasaki Shikibu” born = ”974”><line>This life of ours would not cause you sorrow</line><line>if you thought of it as like</line><line>the mountain cherry blossoms</line><line>which bloom and fade in a day. </line></poem>


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poem

line

line

lineAuthorMurasaki Shikibu

line

born 974

This life of ours would not cause you sorrow

if you thought of it as like

which bloom and fade in a day.

the mountain cherry blossoms

Root node

Element node

Attribute node

The poem is translated from Japanese by Kenneth Rexroth

Text node

Comment node

poem


Node types of XPath 1.0


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3. Entity types

Physical structure of XML documents consists of entities.

An entity is a unit recognized by the XML processor, the content of an entity is text or other kind of data.


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parsed entities -- unparsed entities

internal entities -- external entities

general entities -- parameter entities

3-dimensional categorization:

3. Entity types


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parsed entity

intended to be parsed by the XML processor, content consists of marked-up text

unparsed entity

not intended to be parsed by the XML processor, content can be whatever data

3. Entity types


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internal entity

name and value given in an entity declaration

always a parsed entity

external entity

not internal

parsed or unparsed

3. Entity types


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general entity

used in elements and attributes

parsed or unparsed

internal or external

parameter entity

used in the document type definition

always parsed

internal or external

3. Entity types


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Alternatives

parsed internal parameter

internal general

external parameter

internal general

unparsed external general

3. Entity types


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• root entity, external subset of DTD

• other files intended for XML processing

INPUT FILES for XML processing:

UNPARSED ENTITIES:

XMLprocessor

Information about: application

• elements and attributes

• comments• processing instructions• character data• namespaces• notations and

locations of unparsed entities

• files not intended for XML processing but referred to by entity references in the INPUT FILES

INTERNAL ENTITIES:

• name and textual content given in DTD

3. Entity types


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4. Entity declarations and references

EntityDecl ::= GEDecl | PEDecl

GEDecl ::= '<!ENTITY' S Name S EntityDef S? '>'

PEDecl ::= '<!ENTITY' S '%' Name S PEDef S? '>'

EntityDef ::= EntityValue | ( ExternalID NDataDecl?)

PEDef ::= EntityValue | ExternalID

entity definition for external entityentity definition for internal entity


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internal entity

name and value ( = literal value) given

<!ENTITY % Shape "(rect | circle | poly | default )">

<!ENTITY JY "Jyväskylän yliopisto">

name literal value



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name and system identifier (possibly together with public identifier) given, for an unparsed entity also notation

external entity

<!ENTITY % HTMLsymbol PUBLIC "-//W3C//ENTITIES Symbols for XHTML//EN"

"xhtml-symbol.ent"><!ENTITY % HTMLspecial PUBLIC "-//W3C//ENTITIES Special for XHTML//EN"

"xhtml-special.ent">http://www.w3.org/TR/2002/REC-xhtml1-20020801/dtds.html

Declarations from XHTML specification:

<!ENTITY virtuaaliyliopistouutiset SYSTEM "http://virtuaaliyliopisto.jyu.fi/kotisivut/sisalto/etusivu/newsfeed.xml">



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Unparsed entity

notation name

The notation must have been declared, for example:

<!ENTITY image1 SYSTEM "../images/birdnest.gif” NDATA gif>


<!NOTATION gif PUBLIC "-//ISBN 0-7923-9432-1::Graphic Notation//NOTATION CompuServe Graphic Interchange Format//EN" >


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References to parameter entities:

%Shape;

&JY;

%HTMLsymbol;

&virtuaaliyliopistouutiset;

References to parsed general entities:

Reference to an unparsed general entity:

<poem image="image1">

The type of the attribute has to be ENTITY or ENTITIES



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In addition to entity references, XML documents may contain character references.

Refers to a specific character of Unicode

Provides a decimal or hexadecimal representation of the character’s code point in Unicode

"Example:

One-character entity defined: <!ENTITY quot """>



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Where an entity or character reference can occur?

reference to

can occur inparameter entity ‣document type definition

parsed general entity ‣element content‣attribute value (either in the start-

tag or in the attribute definition)‣entity value

unparsed general entity ‣attribute value (either in the start-tag or in the attribute definition)

character ‣element content‣attribute value (either in the start-

tag or in the attribute definition)‣entity value


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5. XML processor treatment of entity references

References to unparsed entities

Validating processor makes the identifiers for the entities and associated notations available to the application.

<poem image=”figure1"><line>Seisoin ikkunassa ja nauroin. Ihana puu.</line><line>Ihana pesä.</line></poem>


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References to parsed entities

Dealing with two kinds of entity values:

literal value - the character string written between quotes in the entity definition

replacement text - derived by replacing the character references and parameter entity references in the literal value by their character values and replacement texts, respectively.

The XML processor replaces the entity reference by its replacement text.



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<!ENTITY rhyme1 "<rhyme xml:lang="fi"><line>Ole aina iloinen</line><line>niin kuin pikku varpunen</line></rhyme>">

replacement text = literal value

entity declaration

entity reference <rhymecollection>&rhyme1; </rhymecollection>

<rhyme xml:lang="fi"><line>Ole aina iloinen</line><line>niin kuin pikku varpunen</line></rhyme>


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<!ENTITY % StyleSheet ”CDATA”> 

<!ENTITY % Text ”CDATA”> 

<!ENTITY % coreattrs ”id ID #IMPLIED class CDATA #IMPLIED

style %StyleSheet; #IMPLIED title %Text; #IMPLIED”>

http://www.w3.org/TR/2002/REC-xhtml1-20020801/dtds.html


literal value of coreattrs: id ID #IMPLIED class CDATA #IMPLIED

style %StyleSheet; #IMPLIED title %Text; #IMPLIED

replacement text of coreattrs: id ID #IMPLIED class CDATA #IMPLIED

style CDATA #IMPLIED title CDATA #IMPLIED


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<!ENTITY % Block ”(%block; | form | %misc; )*”>

Exercise 10 (Course Text, Chapter 5)

Entity declaration from XHTML Strict-DTD:

What is the (a) literal value(b) replacement text

of entity Block

(a) literal value: (%block; | form | %misc; )*



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Deriving the replacement text of Block : references to parameter entities in the literal value (%block; | form | %misc;)* replaced by their replacement texts.

p | %heading; | div | %lists; | %blocktext; | fieldset | table

Literal value of block:

Replacement text of block:p | h1| h2| h3| h4| h5| h6 | div | ul | ol | dl | pre | hr | blockquote | address | fieldset | table

Literal value of misc : noscript | %misc.inline;

Replacement text of misc : noscript | ins | del | scriptReplacement text of Block : (p | h1| h2| h3| h4| h5| h6 | div | ul | ol | dl | pre | hr | blockquote |

address | fieldset | table | form | noscript | ins | del | script )*



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6. Motivations for the use of entities

• use of non-textual data (audio, graphics, etc.) in XML documents (but can be added also in stylesheets)

• modularization of documents

• consistency

• multiuse of definitions

• adding semantic information by informative entity names and comments attached to entity declarations

The use of entities supports: