Grammars for XML XML Information Set

Transcription

1 Grammars fr XML XML Infrmatin Set Lecture "XML in Cmmunicatin Systems" Chapter 2 Dr.-Ing. Jesper Zedlitz Research Grup fr Cmmunicatin Systems Dept. f Cmputer Science Christian-Albrechts-University in Kiel

2 Recmmended Reading T. Bray, J. Pali, C.M. Sperberg-McQueen, E. Maler, F. Yergeau, J. Cwan (Eds.): XML 1.1 (Secnd Editin), W3C Recmmendatin, 16 August J. Cwan, R. Tbin (Eds.): XML Infrmatin Set (Secnd Editin), W3C Recmmendatin, 4 February N. Luttenberger 2

3 Overview 1. Intrductin 2. Infrmatin items 3. Infrmatin item names (Namespaces) 4. Further infrmatin item prperties N. Luttenberger 3

4 Chapter 2.1 Intrductin

5 Intrductin What is XML Infrmatin Set? A specificatin f abstract data structures describing the cntent f well-frmed XML dcuments accessible t applicatins. A specificatin describing the "utput" f XML prcessrs. A W3C recmmendatin. N. Luttenberger 5

6 Intrductin Frm the XML specificatin: "Each XML dcument has bth a lgical and a physical structure. Lgically, the dcument is cmpsed f, elements, cmments, and prcessing instructins, all f which are indicated in the dcument by explicit markup. (Mre "lgical units" t cme later; NL) Physically, the dcument is cmpsed f [strage] units called entities. " What is the lgical structure f XML dcuments?

7 Intrductin What is an XML infset? "An XML dcument's infrmatin set cnsists f a number f infrmatin items; the infrmatin set fr any well-frmed XML dcument will cntain at least a dcument infrmatin item and several thers. each infrmatin item has a set f assciated named prperties." N. Luttenberger 7

8 Chapter 2.2 Infrmatin Items

9 Infrmatin Items XML dcument attributed, tree-like graph different nde types, e.g.: Rt ("Dcument Infrmatin Item") Dcument element Dcument type declaratin Attribute Prcessing instructin Element Element Element Text Cmment Text N. Luttenberger 9

10 Infrmatin Items Types f infrmatin items Dcument Infrmatin Item Element Infrmatin Items Attribute Infrmatin Items Prcessing Instructin Infrmatin Items Unexpanded Entity Reference Infrmatin Items Character Infrmatin Items Cmment Infrmatin Items Dcument Type Declaratin Infrmatin Item Unparsed Entity Infrmatin Items Ntatin Infrmatin Items Namespace Infrmatin Items N. Luttenberger We ski p m st f t hes e! 10

11 Infrmatin Items Types f infrmatin items Dcument Infrmatin Item Element Infrmatin IsItems the rt f the dcument: It has exactly ne element infrmatin item: the dcument Attribute Infrmatinchild Items element infrmatin item. Prcessing InstructinPrecisely: Infrmatin Items The value f the [dcument element] prperty finfrmatin the dcument infrmatin item is a Unexpanded Entity Reference Items single element infrmatin item. This is called the Character Infrmatindcument Items element infrmatin item. Cmment Infrmatin Items Dcument Type Declaratin Infrmatin Item Unparsed Entity Infrmatin Items Ntatin Infrmatin Items Namespace Infrmatin Items N. Luttenberger 11

12 Excursin: Terminlgy Incnsistent terminlgy between the DOM, XML, and XPath specs "There is cnfusin between the terms tp level (dcument) element (which is an element nde) with rt f the dcument (which is nt)." Clarificatin: N. Luttenberger The rt represents the dcument itself. The dcument element is the element that has all ther elements within the dcument as descendants. The rt can have ther children besides the dcument element, e.g. cmments and prcessing instructins. 12

13 Infrmatin Items Types f infrmatin items Dcument Infrmatin Item Element Infrmatin Items Attribute Infrmatin Items There is an element infrmatin item fr each Prcessing Instructin Infrmatin Itemsin the XML dcument. element appearing Unexpanded Entity Reference Infrmatin Items Character Infrmatin Items Cmment Infrmatin Items Dcument Type Declaratin Infrmatin Item Unparsed Entity Infrmatin Items Ntatin Infrmatin Items Namespace Infrmatin Items N. Luttenberger 13

14 Infrmatin Items Types f infrmatin items Dcument Infrmatin Item Element Infrmatin Items Attribute Infrmatin Items Prcessing Instructin Infrmatin Items There is an attribute infrmatin item fr each Unexpanded Entity Reference Infrmatin attribute (specified ritems defaulted) f each element in the dcument, including thse which Character Infrmatin Items are namespace declaratins. The latter Cmment Infrmatin Items hwever appear as members f an element's Dcument Type Declaratin Infrmatin Item prperty rather than [namespace attributes] its [attributes] Unparsed Entity Infrmatin Items prperty. Ntatin Infrmatin Items Namespace Infrmatin Items N. Luttenberger 14

15 Infrmatin Items Types f infrmatin items Dcument Infrmatin Item Element Infrmatin Items Attribute Infrmatin Items There is a character infrmatin item fr each data Prcessing Instructin Infrmatin Items character that appears in the dcument Each character is a lgically separate infrmatin item, Unexpanded Entity Reference Infrmatin Items but XML applicatins are free t chunk characters Character Infrmatin Items int larger grups as necessary r desirable. (In this lecture, we prefer a text infrmatin item.) Cmment Infrmatin Items Dcument Type Declaratin Infrmatin Item Unparsed Entity Infrmatin Items Ntatin Infrmatin Items Namespace Infrmatin Items N. Luttenberger 15

16 Infrmatin Items Types f infrmatin items Dcument Infrmatin Item Element Infrmatin Items Attribute Infrmatin Items Prcessing Instructin Infrmatin Items Unexpanded Entity Reference Infrmatin Items Character Infrmatin Items Cmment Infrmatin Items Dcument Type Declaratin Infrmatin Item Unparsed Entity Infrmatin EachItems element in the dcument has a namespace infrmatin item fr each namespace that is in Ntatin Infrmatin Items scpe fr that element. Namespace Infrmatin Items N. Luttenberger 16

17 Chapter 2.3 Infrmatin Item Names (Namespaces)

18 Infrmatin Item Names Remember: "An XML dcument's infrmatin set cnsists f a number f infrmatin items; the infrmatin set fr any well-frmed XML dcument will cntain at least a dcument infrmatin item and several thers. each infrmatin item has a set f assciated named prperties." Three imprtant name-related prperties lcal name expanded name namespace URI N. Luttenberger 18

19 Infrmatin Item Names Prblem Hw t prvide unique names, when "mixing" XML dcuments? N. Luttenberger 19

20 <?xml versin="1.0" encing="utf-8"?> <Bk> <ISBN> </ISBN> <authr>kevin Davies</authr> <title>cracking the Genme</title> <price>20.00</price> </Bk> "lcal names" <?xml versin="1.0" encding="utf-8"?> <html> <head> <title>my hme page</title> </head> <bdy> <p>my hbby</p> <p>my bks</p> </bdy> </html>

21 <?xml versin="1.0" encding="utf-8"?> <html> <head> <title>my hme page</title> </head> <bdy> Remark: This is called "mixed cntent" <p>my hbby</p> text cntent and element cntent <p>my bks <Bk> <ISBN> </ISBN> <authr>kevin Davies</authr> <title>cracking the Genme</title> <price>20.00</price> </Bk> </p> </bdy> </html> Bth XML validatr and applicatin prgram Bth XML validatr and applicatin prgram need cntext infrmatin t distinguish between HTML page title and bk title!

22 Namespaces Hw the web wrks Individually created dcuments Distributed creatin f knwledge and lazy integratin Prblem: Vcabulary cllisins! Tw-step slutin 1. Expand lcal names by lcally unique name prefixes 2. Bind lcal prefixes t glbally unique URIs

23 <?xml versin="1.0" encding="utf-8"?> <xhtml:html> <xhtml:head> <xhtml:title>my hme page</xhtml:title> </xhtml:head> <xhtml:bdy> lcally unique <xhtml:p>my hbby</xhtml:p> "expanded names" <xhtml:p>my bks <b:bk> <b:isbn> </b:isbn> <b:authr>kevin Davies</b:authr> <b:title>cracking the Genme</b:title> <b:price>20.00</b:price> </b:bk> </xhtml:p> </xhtml:bdy> </xhtml:html>

24 Namespaces b:bk b:price b:isbn xhtml:head xhtml:p b b:title b:authr xhtml:html xhtml xhtml:title xhtml:bdy vcabulary b vcabulary xhtml But wh guarantees uniqueness f prefixes?

25 Namespaces Give prefixes nly lcal relevance in an instance dcument Assciate lcal prefix with glbal namespace name: a unique name fr a namespace Uniqueness is guaranteed by using a URI (preferably URN) in dmain f the party creating the namespace. URI desn t have any meaning, i.e. desn t have t reslve int anything. An XML namespace is a cllectin f names, identified by a URI reference, which are used in XML dcuments as element and attribute names.

26 <?xml versin="1.0" encding="utf-8"?> <xhtml:html xmlns:xhtml=" xmlns:b=" <xhtml:head> <xhtml:title>my hme page</xhtml:title> </xhtml:head> "namespaces" <xhtml:bdy> <xhtml:p>my hbby</xhtml:p> <xhtml:p>my bks <b:bk> <b:isbn> </b:isbn> <b:authr>kevin Davies</b:authr> <b:title>cracking the Genme</b:title> <b:price>20.00</b:price> </b:bk> </xhtml:p> </xhtml:bdy> </xhtml:html>

27 <?xml versin="1.0" encding="utf-8"?> <xhtml:html xmlns:xhtml=" <xhtml:head> <xhtml:title>my hme page</xhtml:title> </xhtml:head> <xhtml:bdy> <xhtml:p>my hbby</xhtml:p> <xhtml:p>my bks <b:bk xmlns:b=" <b:isbn> </b:isbn> <b:authr>kevin Davies</b:authr> <b:title>cracking the Genme</b:title> <b:price>20.00</b:price> </b:bk> </xhtml:p> </xhtml:bdy> </xhtml:html>

28 <?xml versin="1.0" encding="utf-8"?> <xhtml:html xmlns:xhtml=" <xhtml:head> <xhtml:title>my hme page</xhtml:title> </xhtml:head> <xhtml:bdy> <xhtml:p>my hbby</xhtml:p> <xhtml:p>my bks <Bk xmlns=" <ISBN> </ISBN> <authr>kevin Davies</authr> <title>cracking the Genme</title> <price>20.00</price> </Bk> </xhtml:p> </xhtml:bdy> </xhtml:html>

29 <?xml versin="1.0" encding="utf-8"?> <html xmlns=" <head> <title>my hme page</title> </head> <bdy> <p>my hbby<p> <p>my bks <Bk xmlns=" <ISBN> </ISBN> <authr>kevin Davies</authr> <title>cracking the Genme</title> <price>20.00</price> </Bk> </p> </bdy> </html>

30 Namespaces What d namespace URI s pint t? The "abstractin" camp A namespace URI is the id fr a cncept, it shuldn t reslve t anything The "rthdx" camp It shuld reslve t a schema (xml schema) The "liberal" camp It shuld reslve t many things

31 Chapter 2.4 Further Infrmatin Item Prperties

32 Infrmatin Item Prperties Prperties depend n type f infrmatin item e.g. element infrmatin item [namespace name], [lcal name], [prefix] [children] An rdered list f child infrmatin items, in dcument rder. This list cntains element, prcessing instructin, unexpanded entity reference, character, and cmment infrmatin items [attributes] An unrdered set f attribute infrmatin items, ne fr each f the attributes [namespace attributes] An unrdered set f attribute infrmatin items, ne fr each f the namespace declaratins [base URI] The base URI f the element. [parent] The dcument r element infrmatin item which cntains this infrmatin item in its [children] prperty. N. Luttenberger 32

33 Infrmatin Item Prperties Prperties depend n type f infrmatin item e.g. attribute infrmatin item [namespace name], [lcal name], [prefix] [nrmalized value] The nrmalized attribute value [specified] A flag indicating whether this attribute was actually specified in the start-tag f its element, r was defaulted [attribute type] An indicatin f the type declared fr this attribute in the DTD. Legitimate values are ID, IDREF, IDREFS, ENTITY, ENTITIES, NMTOKEN, NMTOKENS, NOTATION, CDATA, and ENUMERATION. Applicatins shuld treat n value and unknwn as equivalent t a value f CDATA. The value f this prperty is nt affected by the validity f the attribute value. [references] Fr attributes typed IDREF, IDREFS, ENTITY, ENTITIES, r NOTATION [wner element] The element infrmatin item which cntains this infrmatin item in its [attributes] prperty. N. Luttenberger 33