XML Technologies for Next Generation Packaging Technologies

1
XML Technologies for Next Generation Packaging
Technologies

• Lou Reich
• 21-May-2001

2
Overview

• History/Current Status
• Key XML Related Technologies
• Some example XML Snippets

3
History and Status
4
SFDU DTD (1 of 3)

• lt!--XEDU - Exchange Data Unit - Z Class --gt
• lt!ELEMENT XEDU ((XEDUXADUXDDUCommentRclassCcl
  assIclassSclassDclassEclassKclassVclass))gt
•  
• lt!ELEMENT Comment (PCDATA)gt
•  
• lt!--XADU - Application Data Unit - U Class --gt
• lt!ELEMENT XADU ((XADURclassCclassIclassSclass
  Kclass))gt
•  
• lt!--XDDU - Data Description Unit - F Class --gt
• lt!ELEMENT XDDU (Cclass,(RclassSclassDclassEclas
  sKclass))gt

5
SFDU DTD (2 of 3)

•  
• lt!ELEMENT Rclass (Stream,(Reftype, ADID,
  Reference, (ADID?,Reference) )? ) gt
•  
• lt!-- Note that we should make Stream as per XSIL
  to allow reading
• in of some standard types for convenience
• --gt
• lt!ELEMENT Stream (PCDATA)gt
•  
• lt!ELEMENT Reftype (PCDATA)gt
•  
• lt!ELEMENT ADID (PCDATA)gt
• lt!ATTLIST ADID Delimiter CDATA "" Delimiterparam
  CDATA "" gt
• lt!ELEMENT Data (PCDATA)gt
•  
• lt!ELEMENT Reference (PCDATA)gt
•  
•  

6
SFDU DTD (3 of 3)

•  
• lt!ELEMENT Cclass (DDUID, (DEDIDDDRIDSUPID))gt
• lt!ELEMENT DDUID (PCDATA)gt
• lt!ELEMENT DEDID (PCDATA)gt
• lt!ELEMENT DDRID (PCDATA)gt
• lt!ELEMENT SUPID (PCDATA)gt
•  
• lt!ELEMENT Iclass (ADID, Data)gt
•  
• lt!ELEMENT Sclass (ADID, Data)gt
•  
• lt!ELEMENT Dclass (ADID, Data)gt
•  
• lt!ELEMENT Eclass (ADID, Data)gt
•  
• lt!ELEMENT Kclass (ADID, Data)gt
•  
• lt!ELEMENT Vclass (ADID, Data)gt
•  

7
Conclusions

• XML Schema is a major advance from DTDs
• XML Schema does not solve all problems
• Binary data efficiency
• Schema evolution
• Semantics modeling
• Panel 2 at combinations of XML Schema and RDF for
  the next version of DEDSL/DDL
• Panel 2 should investigate XML family of
  specifications as a basis for the next generation
  of Panel 2 Standards

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XML Related Standards

• XML 1.0 Encapsulation Self description
• XML NAMESPACES -Scoping, registration,unique ID
  ControlAuthority
• XLINK- links to non XML Objects - Reference
  Objects,general relationships
• RDF - Serialized Entity Relationship MODEL in XML
  Relationships
• DOM - Tree API Standard APIs
• SAX - Event API Standard APIs
• XSLT- Transformations, can do sophisticted
  querying, currently can convert same XML to
  Microsoft Word,Powerpoint, Postscript or PDF.
  Processes/transformations
• XML Schema - Data Schema Structural Semantics
  DEDSL
• SOAP - IETF Distributed Objects Protocol

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Additional Capabilities Desired

• A mechanism to contain relationship information
  and identify the data objects involved (largely
  clarifying those relationships which were
  implicitly defined in the SFDU blue book).
• Allow data objects anywhere on the internet to be
  logically included in the packaging e.g. using
  URL/URI and various X techniques (Xpath, Xlink
  etc).
• A mechanism to identify that, in addition to the
  description of the data object, there are a
  number of uniquely identified decodings which
  should be applied in a particular sequence to
  reverse the encodings which have been applied.
• Example that a data object has been encoded and
  then compressed
• The package should be easily usable within
  applications i.e. at least one well defined
  API/Interface should be defined.
• Proposed for the further future
• Ability to begin to process a single XML file
  object BEFORE it is all received.

10
Key XML Technologies
11
Namespace Concepts

• Unique identifers    The W3C's Namespaces in XML
  Recommendation provides XML users with a way to
  uniquely and controllably identify the
  vocabularies they are using inside of documents.
• Namespace identifiers forged from URIs   
  Namespace identifiers use the URI syntax defined
  in the IETF's RFC 2396. In some regards, URIs are
  just URLs and URNs, but their use as identifiers
  brings both flexibility and complexity.
• Prefixes    Because URIs can be rather verbose,
  and because they can contain characters which
  aren't permitted in XML element names, namespaces
  use prefixes which map to URIs as a convenient
  shorthand. (A default namespace can be used for
  names without prefixes.)
• Scoping    Because documents may contain multiple
  namespaces, and because the possibility of
  collisions between prefixes exists, namespaces
  allow developers to map prefixes to URIs for
  elements and their contents, not just
  document-wide.

12
XML Namespace Issues

• XML 1.0 didn't include namespaces, and neither do
  a lot of people...    Because namespaces are a
  late and optional arrival, there are many
  vocabularies for which there is no namespace.
• Documents without namespaces    The Namespaces in
  XML Recommendation does not require that all XML
  documents use namespaces. Applications need to
  use other mechanisms, like prearrangement,
  DOCTYPE declarations, and vocabulary sniffing to
  determine what kind of document they have.
• Identifying no namespace    The default namespace
  may be declared to have no value, identifying
  that no namespace is associated with non-prefixed
  elements ltnothingness xmlns"" /gt
• Avoid using colons in names    If your XML
  documents don't use namespaces, don't use colons
  in names. XML 1.0, second edition, makes this
  restriction explicit.

13
The URI Debate

• Prelude What is a Namespace?    The W3C had a
  major struggle over the use of namespaces in
  XHTML. One namespace per DTD? Or one for XHTML as
  a whole? Eventually, the one namespace for the
  entire vocabulary approach won, but no real
  definition of 'namespace' emerged.
• URI references vs. absolute URIs    The W3C
  halted many activities for a brief period this
  summer because of deadlock over the meaning, if
  any, of relative URI references in namespaces.
• Why they were included    URI references allow
  the inclusion of fragment identifiers, like
  location, a useful feature for creating multiple
  different namespaces associated with a single
  URI.
• The absolutization problem    Because URI
  references include the possibility of relative
  URLs, namespaces using URIs might change
  identifier if the document moved between
  contexts. On top of that, the mechanisms for
  converting relative URI references to absolute
  URIs may change between URI schemes.
• Comparison as strings or as URIs?    Although
  Namespaces in XML describes the values of xmlns
  attributes as URI references, it specifies
  character-by-character string comparison for
  namespace processing.
• Deprecation as last resort    Although it doesn't
  resolve any of the underlying issues, 1800 public
  messages on XML-URI (on top of many private
  messages) hadn't led to a more sophisticated
  consensus, so the W3C announced that relative
  URIs are deprecated.

14
Namespace For Schema

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!-- File city.xsd --gt
• ltschema targetNamespace"http//www.ccsds.org/pan
  el2/xmls/example"
• xmlnsexhttp//www.opengis.net/examples
• xmlnsxlinkhttp//www.w3.org/1999/xlink
• xmlnssfd" http//www.ccsds.org/panel2/xmls
  /gml"
• xmlns"http//www.w3.org/2000/10/XMLSchema"
• elementFormDefault"qualified" version"2.03"gt

15
Linking In XML

• A Uniform Resource Identifier (URI) names or
  locates a resource
• An XLink defines connections between two or more
  documents identified by URIs
• XPath identifies particular nodes within a
  document
• An XPointer adds an XPath to a URI
• XBase defines the URI against which relative URIs
  are resolved
• XInclude embeds a document identified by a URI
  inside an XML document.

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Xlink Capabilities

• XLinks can do everything HTML links can do and
  quite a bit more, but they aren't supported by
  current applications.
• XLink elements of all types are placed in the
  http//www.w3.org/1999/xlink namespace, normally
  with the xlink prefix.
• Simple links behave much like HTML links, but
  they are not restricted to a single ltAgt tag.
• Linking elements are identified by xlinktype
  attributes. 
• Simple link elements are identified by xlinktype
  attributes with the value simple. 
• Linking elements can describe the resource
  they're linking to with xlinktitle and
  xlinkrole attributes.

17
Xlink Capabilities

• Linking elements can use the xlinkshow attribute
  to tell the application how the content should be
  displayed when the link is activated, for
  example, by opening a new window. 
• Linking elements can use the xlinkactuate
  attribute to tell the application whether the
  link should be traversed without a specific user
  request.
• Extended link elements are identified by
  xlinktype attributes with the value extended.
• Extended links can contain multiple locators,
  resources, and arcs.

18
Xlink Capabilities

• A resource element represents a local, inline
  resource. It is identified by an xlinktype
  attributes with the value resource.
• A locator element represents a remote,
  out-of-line resource. It is identified by an
  xlinktype attribute with the value locator. 
• Both locator and resource elements can be labeled
  by xlinklabel attributes. These labels are used
  to define arcs between resources. 
• A locator element has an xlinkhref attribute
  whose value is the URI ofthe resource it
  locates. 
• Arc elements are identified by xlinktype
  attributes with the value arc.

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Xlink Capabilities

• Arc elements have xlinkfrom and xlinkto
  attributes of IDREF type that identify the
  resources they connect by their labels.
• Arc elements may have xlinkshow and
  xlinkactuate attributes to determine when and
  how traversal of the link occurs. 
• An out-of-line link is a link that does not
  contain any local resources. 
• A linkbase is a document containing multiple
  out-of-line, extended link elements.
• A linkbase is found when a document with an
  extended link with the role xlinkexternal-linkset
  is read

20
XPointer Overview

• XPointer, the XML Pointer Language, defines an
  addressing scheme for individual parts of an XML
  document.
• XLinks point to a URI (in practice, a URL) that
  specifies a particular Resource.
• The URI may include an XPointer part that more
  specifically identifies the desired part or
  element of the targeted resource or document.
• XPointers use the same XPath syntax you're
  familiar with from XSLtransformations to identify
  the parts of the document they point to, along
  with a few additional pieces.

21
XPointer Targets

• The element with a given ID 
• All elements that possess a certain attribute 
• The first element of a certain type
• The last element whose class attribute has the
  value pending.
• The seventh element of a given type
• The first child of the seventh element
• and many more including combinations of these
  addresses...

22
Xlink Issues

• No general-purpose Web browsers or other
  applications support arbitrary XLinks. 
• XLinks have a much broader base of applicability
  than HTML links. They can be used by any custom
  application that needs to establish connections
  between documents and parts of documents, for any
  reason.
• Even when XLinks are fully implemented in
  browsers they may not alway be blue underlined
  text that you click to jump to another page.
• Sun patent issues

23
XML Schema Features(1 of 2)

• Enhanced datatypes
• 37 versus 10
• Can create your own datatypes
• Can define the lexical representation
• Example "This element can contain strings of this
  form ddd-dddd, where 'd' represents a 'digit'".
• Written in XML
• enables use of XML tools and technologies

24
XML Schema Features(2 of 2)

• Object-oriented
• Can extend or restrict a type (derive new type
  definitions on the basis of old ones)
• Database-oriented
• Can define elements with null content
• Can specify element content as being unique and
  scope of uniqueness
• World Wide Web Oriented
• Namespaces
• Distributed Schema
• Can create equivalent elements - e.g., the
  "subway" element is equivalent to the "train"
  element.

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Referencing a schema in an XML instance document
targetNamespace"A"
schemaLocation"A
A/BookCatalogue.xsd"
Geometry.xsd
GMLInstance.xml
- uses elements from namespace A
- defines elements for namespace A
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XML APIs
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XSLT Transforms
28
DOM Interface
29
SAX Interface
30
JAVA Resources (JARS)
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SFDUs Mapped to XML
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SFDU To XML Mappings

• SFDUs emphasize
• Packaging and linking
• Metadata
• K
• S
• E
• D
• Control Authorities
• Automated Processing

33
XML to SFDU Mapping