Part 3. Introduction XML/GML

Transcription

1 1 Part 3 Introduction XML/GML

2 Introduction to XML (acknowledgement goes to A. Östman -University of Gävle) 2

3 Outline 3 XML syntax, elements and attributes XML Schema XSL XPath

4 XML Technologies 4 XML is a language for describing information or data as text. Ideas XML text

5 XML What? 5 XML can be thought of as smart text that contains tags that have meaning to people and software! <title>my new book</title> <author>knut Hampson</author>

6 XML What? 6 <title>my new book</title> <author>knut Hampson</author> XML is a markup language (tags mark entities in the text) that may be used to write and describe other markup languages. XML = extensible Markup Language

7 XML What? 7 <title>my new book</title> <author>knut Hampson</author> Things in angle brackets are called tags They bound elements! </title> indicates closing of the element!! Elements can have modifiers called attributes. <title dated = 11-Jun-2005 >My new book</title> <author>knut Hampson</author>

8 Markup languages 8 It uses tags to label, categorise and organise information extensible Markup Language (XML) is not limited to a particular set of markups (tags) Hypertext Markup Language (HTML) used to display information on web pages Specific set of tags Do not fully conform to the XML rules XHTML transition language between XML and HTML. It follows the syntax rules of XML

9 Relational database table 9 Parcel-ID 24422F0030/00B000 Parcels Owner Area Jan Peeters C0010/00H000 Lies Janssens 7.3 Table Name: Parcel Column names on first row A relational database table can easily be expressed in XML

10 Parcels in XML file 10 <?xml version= 1.0 encoding= utf-8?> <MyDatabase> <Parcel> <Parcel-ID>24422F0030/00B000</Parcel-ID> <Owner>Jan Peeters</Owner> <Area>2.1</Area> </Parcel> <Parcel> <Parcel-ID> 24422C0010/00H000 </Parcel-ID> <Owner>Lies Janssens</Owner> <Area>7.3</Area> </Parcel> </MyDatabase>

11 Important terms 11 Root element <?xml version= 1.0 encoding= utf-8?> <MyDatabase> <Parcel> <Parcel-ID>24422F0030/00B000</Parcel-ID> <Owner>Jan Peeters</Owner> <Area>2.1</Area> </Parcel> End tag <Parcel> <Parcel-ID> 24422C0010/00H000 </Parcel-ID> <Owner>Lies Janssens</Owner> <Area>7.3</Area> </Parcel> </MyDatabase> XML declaration Start tag

12 Attributes 12 Used to provide additional information about an element Are contained within an element tag <Area method= Digitized from map >7.3</Area> Sometimes included in empty elements <Area method= Not available /> Equal to <Area method= Not available ></Area>

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14 Why XML? 14 Self documenting. People can read and understand the data. Standard tools can be used no need to create custom tools to read/display data. Standard tools ensure data integrity. Can leverage a whole world of XML technologies and tools! Easy to integrate different kinds of data.

15 Why XML? 15 With binary encodings, users & programmers must spend many hours reading & understanding documentation XML documents are self documenting People can read and understand the data!

16 Why XML? 16 Standard tools can be used to read and process XML data. Your programmers don t need to create special custom tools. With XML we can use standard tools like Xerces, XMLSpy/Altova, oxygen XML, MSXML, etc. XML Data XML Parser XML Data in form that can be used by applications Data Structure Description

17 Why XML? 17 Land Title Description Parcel Geometry Utility Connections Taxes owing XML allows any kind of data to be mixed together in-line

18 Why XML? 18 Land Title Parcel Geometry Utilities Taxation Or using complex linked associations. XML allows any kind of data to be mixed together

19 Validation of XML files 19 Well formed XML document adhere to the general XML rules Valid XML documents follow semantic rules The grammar of an XML documents Tells an application and people what each element means and how to use it Specify rules that a large set of documents must follow

20 What is XML DTD? 20 Document Type Definition A data description language developed for XML documents, it defines the document structure with a list of legal elements and attributes It is being replaced by XML Schema!

21 What is XML Schema? 21 Powerful data description language, it describes the structure of an XML document: defines elements that can appear in a document defines attributes that can appear in a document defines which elements are child elements defines the order of child elements defines the number of child elements defines whether an element is empty or can include text defines data types for elements and attributes defines default and fixed values for elements and attributes XSD = XML Schema Definition More precise than DTD, it is the workhorse of XML

22 Database schema 22 TableName ColumnName ColSeq Type Parcel Parcel-ID 1 String Parcel Parcel Owner Area 2 3 String Float Database schemas are often stored in tables Schemas can be expressed in XML

23 Hierarchical structure 23 <?xml version= 1.0 encoding= utf-8?> <MyDatabase> <Parcel> <Parcel-ID>24422F0030/00B000</Parcel-ID> <Owner>Jan Peeters</Owner> <Area>2.1</Area> </Parcel> <Parcel> <Parcel-ID> 24422C0010/00H000 </Parcel-ID> <Owner>Lies Janssens</Owner> <Area>7.3</Area> </Parcel> </MyDatabase>

24 Tree structure 24 Document MyDatabase Parcel Parcel Parcel-ID 24422F0030 /00B000 Owner Jan Peeters Area 2.1

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32 extensible Stylesheet Language (XSL) 32 For converting XML files XSL Transformations (XSLT) for converting documents XSL Formatting Objects (XSL-FO) for formatting for devices that want to display XML We will here use it for transforming it into XHTML, for display in web browsers

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41 XML Path Language (XPath) 41 We use software that does something with the XML files XPath tells software where to go in a XML document To specify a part of the document that needs to be transformed (XSLT etc) To be able to point at a certain part of the document (XPointer, XML Query Language etc)

42 XPath trips 42 Starting point (context node) The journey itself Consists of a number of directions and steps Steps separated by a forward slash (/) The destination (single node or collection of nodes)

43 Important XPath nodes 43 Root node Element nodes Attribute nodes

44 The journey 44 Two types of syntax Child::Parcel[position()=1] Parcel[1] Child, parent, descendant, ancestor Moves up and down in the tree Sibling on the same level Nodetests can be made Often on name of the node

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49 49 More info on XML can be found on:

50 Introduction to GML (acknowledgement goes to Ron Lake - Galdos Systems and A. Östman - University of Gävle) 50

51 Outline 51 Understand why GML was created. What problems does it solve? Based on XML technologies GML concepts Spatial Reference Systems

52 The Big Questions 52 How do we build a scalable geographic database for a significant part of the whole world? What categories of objects do we need in that database or databases? How will you keep them up to date? XML is being used as a lingua franca for data transport. How should it be used for Geographic Information? what can we standardize? Today we exchange geographic files (e.g. MIFF, SHAPE) and do cut and paste WHY? - why not geo-spatial transactions?

53 From reality to geographic data 53 Reality: phenomena Universe of : Discourse subset geographic application perceived in context of classified into feature types data capture defining 0:n feature instances

54 From reality to geographic data 54 Reality: phenomena Universe of : Discourse subset Universe of Discourse perceived in context of geographic application Model based on feature types and their properties Conceptual model Feature Catalogue classified into data capture feature types defining 0:n feature instances Conceptual model expressed by a conceptual schema language Data structured in accordance to the application schema Application Schema Data ISO 19109

55 GML Motivation: Environmental Protection Case: Australia 55 State National Local Governments Private Corporations Distributed & Autonomous Stakeholders! Dynamic changing situation Complex Situation Hard to know what is happening!

56 GML Motivation Integrated Cadastre 56 Municipalities share common borders Features cross from one municipality to another None of this data is STATIC Municipalities in a State or Province Municipalities are merged and divided AND need to use this cadastral data with many other kinds of data

57 GML Motivation Common Characteristics 57 Many kinds of objects things to deal with. Objects are related to one another, often in complex ways Pictures and maps are not enough. Multiple sources and owners of data multiple views Stakeholders are geographically distributed and autonomous Connected and Disconnected participants Dynamic Data Dynamic Situations. Objects live a long time data must live a long time Transactions (often long) are critical. Integration is key to decision making and response Data transactions may go in many directions

58 GML Approach A hierarchy of agreement 58 We agree to use GML GML Model GML Core Schemas Most of us use GML core objects Some of us share application vocabulary Some create their own core objects e.g. OLS, G-XML, LandGML Some of us share application vocabulary Most of us use GML core objects Ordnance Survey, UKHO, MNR GML Application Schemas Nautical charting (S-57), Land Survey, ITS

59 Geometry Object GML Approach Feature Relationships and Linking Geometry Object Geometry Object 59 Feature Object (e.g. Road) crosses Feature Object (e.g. Bridge) atendof Feature Object (e.g. Building) Topology Object Topology Object links express relationships between GML Objects in a file or across the Internet Object relationships model the real world!

60 HTML - Analogy 60 HTML Web Browser HTML HTML Web Server HyperLink Web Server HTML MS SQL Server Oracle DBMS

61 The GML Version 61 GML Web Browser GML Web Feature Server Xlink Web Feature Server MS SQL Server Oracle DBMS

62 GML Approach Built for the Internet 62 Insert feature Web Service Web Service Delete feature Update feature Web Service GML enables wide area geo-spatial transactions!

63 Geography Markup Language (GML) 63 First tests in 1999 Version 2 (simple features) Version 3 profiles made (subsets of full GML) GML files are provided by Web Feature Services GML files have to be rendered (styling) for display (remember XSLT?)

64 Based on XML technologies 64 XML, XML Namespaces, XML Schema, XLinks Implements concepts from the ISO standards Support spatial and non-spatial properties of objects Open and vendor neutral

65 XML Technology Summary 65 Technology for Encoding and Data Modeling Expression (DTD, RDF and XSD) The XML Technologies for GML!! Technology for Selecting & Pointing (XPath, XPointer) Technology for Transforming (XSLT) Technology for Linking and Associating (XLink) Technology for Graphical rendering (SVG, VML, X3D)

66 Once Over Lightly What? 66 XML is a whole family of technologies for data handling XML Schema (XSD) XPointer XLink Resource Description Framework (RDF) XSLT SOAP XML SAML (Web Services Description) WSDL SVG (Graphics)

67 What is RDF? 67 Data description language (cf. DTD, XSD). It is oriented to semantics & metadata. Ideas from RDF are used in GML.

68 What is XLink? 68 A language for describing links between XML documents. It is more flexible & robust than HTML linking!

69 What is XPointer? 69 An XML language for pointing to & selecting subtrees of XML documents. It is more precise than HTML pointing.

70 What is XSLT? 70 An XML language developed for transforming XML. It is the basis of XML styling XML can be styled (transformed) into HTML, SVG etc.

71 What is SVG? 71 An XML language for describing 2D drawing. It supports vector drawing in standard browsers.

72 What is SOAP? 72 An XML language for sending messages over the Internet. It is the foundation of web-based services!

73 What is WSDL? 73 An XML language for describing web-based services. It is the foundation of web-based services!

74 GML basic Concepts 74

75 GML: What is it? 75 OGC Endorsed Adopted Specification (GML 3.0 passed January 2003) for encoding spatial information. V3.2.1 implementation standard of ). ISO was prepared by ISO/TC211 jointly with OGC A set of XML technologies for handling spatial data on the Internet. Builds on XML and Web Service Technologies. Emerging international standard for spatial data endorsed by companies and agencies around the world. Converged with G-XML (Japan) G-XML 3.0 is GML. Other GML Languages (SensorML, O&ML, XMML) under development.

76 Why GML? 76 A lingua franca for geographic information. GML data can be read and understood by people. GML can enable distributed spatial datasets that are linked together local maintenance & development /global access. Reduced cost for data. GML data can easily be mixed with non-spatial data including text, video, and imagery. (e.g. work order) GML can build shareable application schemas for telecommunications, utilities, forestry, tourism, and location-based services. GML focusses on content, it separates content and presentation (SVG)

77 Why GML? 77 GML is easily transformed coordinate conversion etc. Services can be created with specific types and then easily discovered. Services that act on features. Services that return routes or tracks. GML provides a STANDARD means to define input & output arguments. GML is non-proprietary and open! Any client can talk to any server! GML enables non-proprietary web feature servers, image/map annotation, map styling and spatial analysis.

78 GML: Conclusion 78 Scope of GML A modelling language for geographic information An encoding for geographic information Designed for the web and web-based services GML is An open standard Enabling a vendor neutral exchange of spatial data Ready for Service oriented architectures.

79 Example 79 Road name: E4 class: European centerline gml:curve maintainer: NRA 79

80 GML example 80 <Road gml:id= o.1fg7a3 > <name>e4</name> <class>european</class> <centerline> <gmlcurve> </gmlcurve> </centerline> <maintainer>nra</maintainer> </Road> GML Objects are XML Elements

81 Kinds of GML Objects 81 Features Coverages

82 Kinds of GML Objects 82 Geometries Topologies

83 Kinds of GML Objects 83 Observations Values

84 Kinds of GML Objects 84 Coordinate Referencing Styles

85 Kinds of GML Objects 85 Dynamic Features Time Objects

86 GML Features 86 FeatureType (person) Feature represents some real world domain object that may have spatial characteristics name description age height weight

87 GML Features 87 Feature types in GML are represented by element names <element name = Church type = ChurchSchema /> <complextype name = ChurchSchema > <sequence> <element name = denomination type= string /> <element name = numberrooms type= integer /> <element ref = gml:locationof /> </sequence> </complextype>

88 Granville Street Feature Relationships 88 GML can capture associations in-line or via links. Granville intersects Georgia Georgia Street Georgia intersects Granville The association can be a first class object (feature) with its own properties!

89 Remote Properties/Associations 89 <Road fid = georgia > <gml:centerlineof> </gml:centerlineof> <numlanes>4</numlanes> <class>street</class> <intersects xlink:type = simple xlink:href = #granville /> </Road> <Road fid = granville > <gml:centerlineof> </gml:centerlineof> <numlanes>4</numlanes> <class>street</class> <intersects xlink:type = simple xlink:href = #georgia /> </Road> Remote Association Remote Association

90 GML example with XLink 90 <Road gml:id= o.1fg7a3 > <name>e4</name> <class>european</class> <centerline> <gml:curve> </gml:curve> </centerline> <maintainer xlink:href= urn:x-auth:o.1f7d6e /> </Road>

91 Remote Properties/Associations 91 GML Interprets an xlink:href on a GML Property to mean that the value of the property is the resource referenced in the link. The xlink:href could point to a resource within the GML document or anywhere on the internet. Remote properties can also be seen as associations between feature instances.

92 Feature Collections 92 A GML feature collection is a logical or physical collection of GML feature instances e.g. Province of British Columbia e.g. a query result A Feature Collection must derive from gml:abstractfeaturecollectiontype

93 GML Geometry Classes 93 Point Line String Polygon (linear) MultiPoint MultiLine String MultiPolygon MultiGeometry

94 Geometry model (Simple features) 94

95 Point example 95 <Point gid= P1 srsname= urn:opengis:crs:epsg::28992 > <coord> <X>56.1</X> <Y>0.45</Y> </coord> </Point> 95

96 Line String example 96 <LineString gid= L1 srsname= urn:opengis:crs:epsg::28992 > <coord><x>0.0</x><y>0.0</y></coord> <coord><x>20.0</x><y>35.0</y></coord> <coord><x>100.0</x><y>100.0</y></coord> </LineString> 96

97 Polygon example 97 <Polygon gid="_98217" srsname= urn:opengis:crs:epsg::28992 > <outerboundaryis> <LinearRing> <coordinates>0.0, , , , ,0.0</coordinates> </LinearRing> </outerboundaryis> <innerboundaryis> <LinearRing> <coordinates>10.0, , , , ,10.0</coordinates> </LinearRing> </innerboundaryis> <innerboundaryis> <LinearRing> <coordinates>60.0, , , , ,60.0</coordinates> </LinearRing> </innerboundaryis> </Polygon> 97

98 Geometry Properties 98 GML provides the notion of a geometry property. Geometry properties are geometry-valued. The property name describes property role in relation to the feature! e.g. <Church fid = StLukes12 > <gml:locationof> <gml:point srsname =.. > </gml:locationof> </Church> </gml:point>

99 GML Geometry 99 GML 2. Supported only Linear Geometries. Still available in GML 3.0 GML 3.0 based on ISO TC/ GML 3.0 provides many more geometry classes including: 0D, 1D, 2D and 3D geometries. Composite curves, surfaces and solids. Curve primitives (segments) including arcs, arc strings, beziers, bsplines. Surface primitives including polygonpatch, triangle and rectangle Coordinate strings (various forms) GML coordinate interpretation based on CRS dictionary reference. GML Data CRS Dictionary CRS Definition

100 GML Topology 100 New in GML based on ISO TC/ GML 3.0 provides standard topology objects: Nodes, Edges, Faces and Solids Boundary and Co-boundary relationships with orientation. Topology Complexes. Topological expressions. Boundary and Co-boundary relationships with orientation. Geometric realization of any topological element. GML Data Topology Geometry Geometry object

101 GML - Spatial Reference Systems 101 What is meant by srsname= urn:opengis:crs:epsg::28992? Specifications of Spatial Reference Systems have been collected by the European Petroleum Survey Group (EPSG) Their database is now maintained by the Intenational Association by Oil and Gas Producers (OGP),

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103 Performance Issues 103 GML is text! Without compression data volumes can be significant. Example: Vancouver (City Center) has 2186 features and takes megabytes. (270 bytes/feature) (54 bytes zipped) Example: Vancouver (Greater City) has features and takes 25 megabytes. (340 bytes/feature) (68 bytes zipped) Example: Lutheran County, Pennsylvania, USA, has 4800 features and takes 3.9 megabytes (830 bytes/feature) (166 bytes zipped) Good news: The data is very compressible. Experiments with GZIP have provided compression factors of 5-7:1; XML-specific compression (e.g. BinXML) can improve on this by a factor of 2 more. Updating a WFS at features second.

104 Implications of GML 104 Makes it possible to build a spatial infrastructure reduces the incremental cost of building application specific data sets. Makes it easier to integrate spatial information with nonspatial information me a map I can interact with! => Better utilization of spatial information. Leads to geographic standards for all kinds of applications standard shareable vocabularies lowers cost of data sharing and increases interoperability. Provides a flexible, open, standard transport for geographic information for location-based applications. Allows vendors to focus on content, performance and usability features!

105 Other Information 105 OGC Web Site ( - GML v3.0 and v3.1 est_practices_guide.pdf