snu oopsla lab. hypertext links(xll) © copyright 2001 snu oopsla lab

SNUOOPSLA Lab.

Hypertext links(XLL)

© copyright 2001 SNU OOPSLA Lab.

SNU

OOPSLA Lab.

Contents

• Concepts• XML syntax basic links• XML linking specification• URLs• Link behavior• Extended pointers• Attribute name conflicts• Link value strategies

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Basic Link

• Source– a phrase that directs the reader’s attention

to other information• Target

– is located at the start of the required text

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Terminology

• Resource– target object

• Linking element– source

• Traversal– the act of moving from the liking element to

the resource

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Terminology(Cont’d)

• Simple link– the primitive one-directional linking

scheme, but make it possible to traverse links between documents

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URLs

• Objects are identified using the URL mechanismSee <link target=“MyServe.MyCorp.com/xml/Doc9#X123”>

Details</link>

…

</chapter>

<chapter ident=“X123”>

<title> Details </title>

<p> The details are …

</chapter>

...

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Attributes in the Linking Element

• Attributes in the linking element can influence– the means by which a link can be activated

• a link could be activated by the person(‘user’ link)• directly by the application(‘auto’ link)

– the presentation technique required once it has been activated

• application may jump to the specified resource(‘replace’)

• display the resource in another window(‘new’)• insert the resource into the original text(‘embed’)

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Extended Link

• Extended link– resources can be cross-related– an extended link contains a number of

locator elements, each one points to a resource

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Out-of-line Link

• Out-of-line link– provides facility of separating the extended

link from all the resources it defines– may physically appear in-line, in the sense

that it is placed in the flow of text– a more obvious place to put out-of-line

links is at the top of the document

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Extended Link Group

• Extended link group– a number of extended document pointers

are used to identify all the inter-linked documents

– they are contained in an extended group element

=> all the documents concerned are deemed to be pointers to each other

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XML syntax basic links

<!ELEMENT section (…)>

<!ATTLIST section target ID #REQUIRED>

<section target=“s”>

<title>This is Section 6</title>

…

</section>

<!ELEMENT xref (…) >

<!ATTLIST xref link IDREF #REQUIRED>

<para>Please refer to

<xref link=“s6”>Section 6</xref>

for more details</para>

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Identifying links

• Assumes– advanced linking features described here are not

inherent in the XML syntax– so are not based on reserved attribute types– an XML parser is therefore unable to validate the links– there is another layer of software, an ‘XML link

processor’• interrogates the parsed document instance, and

possibly also the DTD to detect and activate linking feature

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Identifying links(Cont’d)

• If no DTD, the reserved attributes may be stored in the document

<link xml-link=“simple” href=“…”>the link</link>

• When a DTD is used, this information is stored in the attribute declaration

<!ATTLIST link xml-link CDATA #FIXED “simple”

href CDATA #REQUIRED>

<link href=“…” >the link</link>

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Simple Links

• Simple link – contains only one resource locator– only the Href and xml-link attributes are required– any name can be chosen for the linking element

See <simple href=“…”>book 9</simple> for details

<!ATTLIST simple xml-link CDATA #FIXED “simple”>

<simple href=“http://ProcMan.xml#Sec9” xml-link=“simple”>

See Section 9 of the Procedures Manual

</simple>

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Title and Role• Title

– it is useful for simple links to be labeled, so that the user can decide whether it would be profitable to follow the link

<!ATTLIST link …title CDATA #IMPLIED>

… are you going to<link href=“#X123” title=“Location”>Scarborough</link> fair?

• Role– is used to create categories of link that can be accessed by specialized

browsers<!ATTLIST link …

role CDATA #IMPLIED>… are you going to

<link href=“#X123” role=“describe”>Scarborough</link> fair?

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Extended Links

• Extended links– refer to a number of resources by including embedded

resource locators– each locator is stored in a locator element– all related locator elements are grouped within an extended

element– the DTD author must ensure that the extended element can

contain the locator element, as well as any DTD specific elements appropriate at this point

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Extended Links(Cont’d)

<!ELEMENT para (#PCDATA | extend | emph)>

<!ELEMENT extend (#PCDATA | locate | emph)>

<!ATTLIST extend xml-link=“extended” … >

<!ELEMENT locate (#PCDATA)>

<!ATTLIST locate xml-link=“locator” …>

<para>Here are

<extend>some <emph>extended</emph>

links:

<locate href=“…”>Locator 1</locator>,

<locate href=“…”>Locator 2</locator>

</extend>

</para>

Here are some extended links: Locator1, Locator2.

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Content Role and Content Title

• Content role and content title– locators in extended links are labeled with

the title attribute– extended link itself, if it is an in-line link,

should also have a title and role

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Content Role and Content Title(Cont’d)

<!ATTLIST extend …

content-role CDATA #IMPLIED

content-title CDATA #IMPLIED>

<song>

<title>Are you going to

<extend content-title=“song” content-role=“reference”>

Scarborough

<locator title=“location” role=“explain” href=“…”/>

<locator title=“history” role=“explain” href=“…”/>

</extend>

fair?</title>

…

</song>

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Out-of-link Links

• In-line links– a link that serves as one of its own resources– a link source that is embedded within the text

• Out-of-line links– a link that does not serve as one of its own

resources– should be considered when

• a read-only document is involved• different links are required for different groups of

people, where seeing other’s links is confusing

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Out-of-link Links(Cont’d)

• The Inline attribute must be set to ‘false’ to identify an out-of-line link

<extend inline=“false”>

<locator href=“…”>Locator 1</locator>

<locator href=“…”>Locator 2</locator>

</extend>

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Extended Link Groups

• Group element– other documents in a group of inter-linked

documents can be identified with steps attribute• contains a value stating how many steps to take

– which contains document element with href attribute

<group steps=“2”>

<document href=“DocumentHub”>Document Hub</document>

</group>

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URLs

• The method for locating entire documents

<link href=“/xml/myfiles/detail.xml”>See details</link>• Linking a specific element in the current file

<link href=“../myfiles/detail.xml#part3”>See details, part 3</link>

– entire document is delivered• Indicating that only referenced part of the document is

required

<link href=“../myfiles/detail.xml|part3”>See details, part 3</link>

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Link Behavior

• Actuate– user: the links only traversed when explicitly selected by the user– auto: the link is activated automatically as soon as the linking

element is presented to the user• Show

– replace: the browser replaces the source text with the resource required

– embed: the resource is brought to and embedded in the source text

– new: the browser opens a new window to display the resource, leaving the original window on-screen

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Link Behavior(Cont’d)

• The show and actuate attributes also appearing in the extended links

<extend show=“new”>

<locate href=“…” />

<locate href=“…” show=“embed” />

</extend>

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Extended Pointers

• XPointer– a mechanism for identifying a designated

resource by its location

• Instructions(location terms) in an XPointer– refer to the element hierarchy tree– include references to siblings, children and

ancestors– are read from left to right

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Extended Pointers(Cont’d)

• Exampleshttp://MyServe.MyCorp.com/

xml/doc9#ROOT()CHILD(3,chap)STRING(7,”Napoleon”,0)

http:// MyServe.MyCorp.com/

xml/doc9?

XML-XPTR=ROOT()CHILD(3,chap)STRING(7,”Napoleon”,0)

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Absolute Locations

• HERE()– identifies the current element(the linking element itself)

• ID()– specifies an element containing an attribute of type ID

ID(sec17)

<section target=“sec17”>…</section>’• HTML()

– specifies the name of an Anchor element in an HTML document

HTML(para3)

<p><a name=“para3”>The third paragraph.</a>…</p>

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Absolute Locations(Cont’d)

• ROOT()– identifies the entire document as the container of

the target resource

• DITTO()– specifies the result of the first search as the

starting-point for this second search

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Relative Locations

• CHILD()– specifies a child of the current element

CHILD(3, .)

<para>…</para> <1

<list>…</list> <2

<para>…</para> <3

CHILD(3, *)

<number>13</number> <1

High Str., <2

<town>NewTown</town> <3

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Relative Locations(Cont’d)

CHILD(1, *CDATA)

<number>13</number>

High Str., <1

<town>NewTown</town>

CHILD(3, para)

<para>…</para> <1

<list>…</list>

<para>…</para> <2

<table>…</table>

<para>…</para> <3

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Relative Locations(Cont’d)CHILD(3, para, status, secret)

<para status=“secret”>…</para> <1

<para status=“SECRET”>…</para> <2

<para status=“normal”>…</para>


<para status=“Secret”>…</para> <3

CHILD(2, para, author, “D. Adams”)

<para author=“D.Adams”>…</para>

<para author=“Dikens”>…</para>

<para author=“D. Adams”>…</para> <1

<para author=“d. adams”>…</para>

<para author=“D. Adams”>…</para> <2

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CHILD(3, para, status, *IMPLIED)

<para status=“secret”>…</para>

<para>…</para> <1

<para>…</para> <2


<para>…</para> <3

CHILD(3, PARA, STATUS, *)

<para status=“secret”>…</para> <1

<para>…</para>

<para status=“normal”>…</para> <2

<para status=“normal”>…</para> <3

<para>…</para>

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• ANCESTOR()– specifies a search through enclosing elements

• FSIBLING()– identifies a following sibling– to select next element:

<para>…</para><para>…</para> <1

– to select the penultimate element:

<chapter><para>…</para><para>…</para><para>…</para> < -2<para>…</para> < -1</chapter>

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• PSIBLING()– identifies a previous sibling to the current element– to select the previous element

<para>…</para> <1<para>…</para>

– to select the second element in the enclosing element <chapter><para>…</para> < -1<para>…</para> < -2<para>…</para><para>…</para></chapter>

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• DESCENDANT()– indicates an element anywhere within the location

source• FOLLOWING()

– has a similar effect as DESCENDANT, except that it not bounded by the current element’s end-tag, but searches on to the end of the document

• PRECEDING()– initiates a search back through the document,

ignoring document hierarchies

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• STRING()– locates a given letter, word, phrase or other string

of text, such as ‘Napoleon the Emperor’– the first parameter is an occurrence counter– the second parameter is the string to find

STRING(1, ‘Napoleon the Emperor’, 0)

Using the N element for name and Occ for

occupation, “Napoleon the Emperor” is coded… <1

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• STRING()– tags are transparent to the search:




<n>Napoleon</n> the <occ> Emperor</occ> <2– the third parameter is a value specifying an offset from the start of the search

text




<n>Napoleon</n> the <occ> Emperor</occ> <2

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Attribute Name Conflicts

• xml-attribute attribute can be used to rename the others

<!ATTLIST link

xml-attributes CDATA “show xshow”

xshow (embed|replace|new) “replace”>

<!ATTLIST link

xml-attributes CDATA “show xshow title xtitle”

xshow (embed|replace|new) “replace”

xtitle CDATA #IMPLIED>

<!ATTLIST link xml-attributes “href target”

target CDATA #REQUIRED>

<link target=“X123”>…</link>

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Link Value Strategies

• Document authors are usually required to generate identifiers for new objects– simply assign the next available sequential value– assigning the title, or an abbreviation of the title, to

a locator:

<xref idref=“#Summary”>– an abbreviated reference scheme may be

considered

see <xref idref=“#ch7pa12”>Chapter 7, Paragraph 12</xref>

snu oopsla lab. hypertext links(xll) © copyright 2001 snu oopsla lab

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