snu oopsla lab. xml documents 2 : additional issues the ubiquitous xml(3) © copyright 2001 snu...

SNUOOPSLA Lab.

XML Documents 2 : Additional issues

The ubiquitous XML(3)

© copyright 2001 SNU OOPSLA Lab.

2SNUOOPSLA Lab.The ubiquitous XML

Additional Issues

XML Link White space Name space


Contents of XML Link HTML Link vs. XML Link concept of XML Link simple link extended link XPointer

XML Link


HTML Link vs. XML Link HTML Link

URL 은 하나의 문서전체만을 가리킬 뿐 , 문서 내 부분을 가리킬 수 있는 방법이 없다 . Document 들 사이의 연관성에 대한 개념이 없다 . 한 방향 LINK 만 가능하다

XML Link document 의 임의의 위치를 가리킬 수 있는 방법제공 다양한 element 를 link 할 수 있다 . (cf. ‘A’ element in

HTML) 다방향 Link 참조 , 주석 , 각주 등을 쉽게 처리할 수 있다 .


Concept of Xlink (1/12) XLL (eXtensible Linking Language)

Xlink define how one document link another

document in fact, URL(URI)

Xpointer define how one document link the component

of documents


Concept of Xlink (2/12) 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>

XML Link


Concept of Xlink (3/12) Source

a phrase that directs the reader’s attention to other information

Target is located at the start of the required

text

XML Link


Concept of Xlink (4/12) Resource

target object Linking element

source Traversal

the act of moving from the liking element to the resource

See <link> More Information</link> for details.

linking element

<chapter><title>More Information</title><p>The details are……</chapter>

resource

traversal

XML Link


Concept of Xlink (5/12) 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>...

Doc9xml

MyServe server

MyCorp

XML Link


Concept of Xlink (6/12) 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?

XML Link


Concept of Xlink (7/12) 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

XML Link


Concept of Xlink (8/12)<!ATTLIST extend …

content-role CDATA #IMPLIEDcontent-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>

Are you going to Scarborough fair?

locationhistory

A popular seaside town in Yorkshire is Scarborough history

song

XML Link


Concept of Xlink(9/12)

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>

XML Link

URL


Concept of Xlink (10/12) Link Behavior (1/2)

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

XML Link


Concept of Xlink (11/12) Link Behavior(2/2)

The show and actuate attributes also appearing in the extended links<extend show=“new”><locate href=“…” /><locate href=“…” show=“embed” /></extend>

XML Link


Concept of Xlink (12/12) Simple link

the primitive one-directional linking scheme, but make it possible to traverse links between documents

Extended link multi-directional linking scheme an extended link contains a number of locator

elements, each one points to a resource

XML Link


Simple Link 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’)

XML Link


Extended Link (1/8) resources can be cross-related an extended link contains a

number of locator elements, each one points to a resource

XML Link


Extended Links (2/8) 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

XML Link


Extended Links (3/8)<!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.

XML Link


Extended Link (4/8) 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

XML Link


Extended Link (5/8) 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

XML Link


Extended Link (6/8) 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>

resourceresource

Document A Document B

XML Link


Extended Link (7/8) Extended link group(1/2)

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

XML Link


Extended Link (8/8) Extended link group(2/2)

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>

XML Link


Xpointer (1/13) 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

XML Link


Xpointer (2/13) Examples

http://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)

XML Link


Xpointer (3/13) Absolute Locations(1/2)

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

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

XML Link


Xpointer (4/13) Absolute Locations(2/2)

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

XML Link


Xpointer (5/13) Relative Locations(1/9)

CHILD() specifies a child of the current element

CHILD(3, .)<para>…</para> <1<list>…</list> <2<para>…</para> <3

CHILD(3, *)<number>13</number> <1High Str., <2<town>NewTown</town> <3

XML Link


Xpointer (6/13)

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

XML Link

Relative Locations(2/9)


Xpointer (7/13)CHILD(3, para, status, secret)<para status=“secret”>…</para> <1<para status=“SECRET”>…</para> <2<para status=“normal”>…</para><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

XML Link



Xpointer (8/13)

CHILD(3, para, status, *IMPLIED)<para status=“secret”>…</para><para>…</para> <1<para>…</para> <2<para status=“normal”>…</para><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>

XML Link



Xpointer (9/13) 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>

XML Link



Xpointer (10/13) 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>

XML Link



Xpointer (11/13)

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

XML Link



Xpointer (12/13)

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

XML Link



Xpointer(13/13) STRING()

tags are transparent to the search:STRING(1, ‘Napoleon the Emperor’, 0)Using the N element for name and Occ for occupation, “Napoleon the Emperor” is coded… <1<n>Napoleon</n> the <occ> Emperor</occ> <2

the third parameter is a value specifying an offset from the start of the search textSTRING(1, ‘Napoleon the Emperor’, 7)Using the N element for name and Occ for occupation, “Napoleon the Emperor” is coded… <1<n>Napoleon</n> the <occ> Emperor</occ> <2

XML Link



Additional Issues



Contents of White space concept Line-end normalization White space in markup Element content space Preserved space Ambiguous space

White space


Concept of white space ‘white space’ is used to describe a

number of miscellaneous characters that have no visual appearance, but in some way affect the formatting of a document

White space


Line-end normalization ASCII standard includes two special

characters, these are the CR and LF characters

XML processor uses the LF character to terminate lines

A sequence of identical line-endcodes are treated separately.

A Macintosh [CR]Data file.[CR]

A Macintosh [LF]Data file.[LF]

A Macintosh [CR][LF]Data file.[CR]{LF}

White space


White space in markup The two examples below are

deemed to be equivalent

<book issue=“3” date=“15/3/97”>

<bookIssue = “3”Date = “15/3/97” >

White space


Element content space Document authors may choose to insert white

space in order to improve the presentation. For example, the second document fragment

below is easier to read than the first:<sec><auth><first>Neil</first><second>Bradley</second></auth>…

<sec><auth>

<first>Neil</first><second>Bradley</second></auth>…

White space


Preserved space A distinction is made between act of leaving all white

space characters intact, and normalizing white space back to a single character.

When left intact, the white space is said to be preserved.

When normalized, it is said to have collapsed. The document author has some control over

normalization of white space in the text, using a reserved attribute named ‘xml:space’.

<para xml:space=“preserve”>Mrs WhiteNewtownEngland</para>

Mrs WhiteNewtownEngland

White space


Ambiguous space Ambiguities may arise as to whether some white

space is intended to be part of the document, or is just present to make the data file more readable

The problem is deciding whether or not the Line-end code after the Paragraph start-tag, or line-end code at the end of the text may be omitted or retained.

Is this line of text : [CR]To be kept separate from this one?

Is this line of text : To be kept separate from this one?

Is this line of text : To be kept separate from this one?

White space


Ambiguous space HTML

All white space between block elements is ignored

SGML Focus is on the line-end codes rather than on white

space in general. RS character identifies and RE character identifies take the roles of record delimiters.

White space


Additional Issues



Contents of Name space Compound Documents The Standard Namespace identification Using name spaces Simplification techniques DTD issues

Name space


Compound Documents It is possible for a single XML document to contain

fragments that are defined in different DTDs.

The well-formed nature of all XML structures makes it relatively simply to embed ‘foreign’ structures in documents. But there are two problems to identify which schema a particular element belongs to. How to avoid duplication of element and attribute names.

Name space


The Namespaces standard was produced by the W3C, and gained recommended status in Jan. 1999.

This standard focuses on two issues It provides a mechanism for identifying the

namespaces used in the document. It identifies which namespace a particular

element or attribute belongs to.

The Standard

Name space


Most standards can now be identified with a specific location on the Web.

The Namespaces standard uses URLs to identify each namespace.

Namespace identification

Name space


Using name spaces Namespaces are defined using attributes.the

attribute name ‘xmlns’ is used to declare a namespace, and at the same time declare the prefix that will stand in for the full URL in element and attribute names.

Attributes from one namespace can be used in elements from another.

<X:html xmlns:X=http://www.w3.org/TR/REC-html40>…<X:p>An HTML paragraph.</X:p>

</X:html>

Name space

http://www.w3.org/TR/REC-html40


Simplification techniques When every element and attribute has a prefix, the

document can become difficult to read, and the extra characters certainly add to its size. Fortunately, Standard includes the concept of a default namespace.

The default namespace can be changed at any point in the document hierarchy.<book xmlns=“file:/DTDs/book.dtd”

xmlns:X=http://www.w3.org/TR/REC-html40> … <X:td></X:td> … … <html xmlns=http://www.w3.org/TR/REC-html40>

… <td> … </td> ... … </html>

<para> . . . </para></book>

Name space




DTD issues In order to parse documents against a DTD, it is

necessary to include the prefixes in the element definitions:

<!ELEMENT document (shoe|boot|slipper|veh:bonnet| veh:boot| veh:wheel)*>

• The namespace definition can also be included in the DTD.• The DTD must also include references to all allowed

children in the element content models, regardless of the namespace they may belong to.

Name space