Modify the following XML document so that it is also a valid RDF document:

Transcription

1 RDF

2 XML --> RDF Modify the following XML document so that it is also a valid RDF document: XML <River id="yangtze" xmlns=" <length>6300 kilometers</length> Yangtze.xml "convert to" RDF <River rdf:id="yangtze" xmlns=" <length>6300 kilometers</length> Yangtze.rdf

3 The RDF Format 1 RDF provides an ID attribute for identifying the resource being described. 2 The ID attribute is in the RDF namespace. <River rdf:id="yangtze" xmlns=" <length>6300 kilometers</length> 3 Add the "fragment identifier symbol" to the namespace.

4 The RDF Format (cont.) 3 1 Identifies the type (class) of the resource being described. These are properties, or attributes, of the type (class). 2 Identifies the resource being described. This resource is an instance of River. <River rdf:id="yangtze" xmlns=" <length>6300 kilometers</length> 4 Values of the properties

5 Best Practice Namespace Convention Question: Why was "#" placed onto the end of the namespace? E.g., xmlns=" Answer: RDF is very concerned about uniquely identifying things - uniquely identifying the type (class) and uniquely identifying the properties. If we concatenate the namespace with the type then we get a unique identifier for the type, e.g., If we concatenate the namespace with a property then we get a unique identifier for the property, e.g., Thus, the "#" symbol is simply a mechanism for separating the namespace from the type name and the property name.

6 The RDF Format <Class rdf:id="resource" xmlns="uri"> <property>value</property> <property>value</property>... </Class>

7 Uniquely Identify the Resource Earlier we said that RDF is very concerned about uniquely identifying the type (class) and the properties. RDF is also very concerned about uniquely identifying the resource, e.g., This is the resource being described. We want to uniquely identify this resource. <River rdf:id="yangtze" xmlns=" <length>6300 kilometers</length>

8 rdf:id The value of rdf:id is a "relative URI". The "complete URI" is obtained by concatenating the URL of the XML document with "#" and then the value of rdf:id, e.g., <River rdf:id="yangtze" xmlns=" <length>6300 kilometers</length> Yangtze.rdf Suppose that this RDF/XML document is located at this URL: Thus, the complete URI for this resource is:

9 xml:base On the previous slide we showed how the URL of the document provided the base URI. Depending on the location of the document is brittle: it will break if the document is moved, or is copied to another location. A more robust solution is to specify the base URI in the document, e.g., <River rdf:id="yangtze" xmlns=" xml:base=" <length>6300 kilometers</length> Resource URI = concatenation(xml:base, '#', rdf:id) = concatenation( '#', "Yangtze") =

10 rdf:about Instead of identifying a resource with a relative URI (which then requires a base URI to be prepended), we can give the complete identity of a resource. However, we use rdf:about, rather than rdf:id, e.g., <River rdf:about=" xmlns=" <length>6300 kilometers</length>

11 Triple -> resource/property/value has a of 6300 kilometers resource property value has a of western China's resource property value has a of East China Sea resource property value

12 The RDF Format = triples! The fundamental design pattern of RDF is to structure your XML data as resource/property/value triples! value of property-a value of property-b <Resource-A> <property-a> <Resource-B> <property-b> <Resource-C> <property-c> Value-C </property-c> </Resource-C> </property-b> </Resource-B> </property-a> </Resource-A> Notice that the RDF design pattern is an alternating sequence of resource-property. This pattern is known as "striping". The value of a property can be a literal (e.g., length has a value of 6300 kilometers). Also, the value of a property can be a resource, as shown above (e.g., property-a has a value of Resource-B, property-b has a value of Resource-C). We will see examples of properties having a resource value in a little bit.

13 Naming Convention The convention is to use a capital letter to start a type (class) name, and use a lowercase letter to start a property name. This helps the eye quickly discern the striping pattern. uppercase lowercase <River rdf:about=" xmlns=" <length>6300 kilometers</length>

14 RDF Model (graph) Legend: Ellipse indicates "Resource" Rectangle indicates "literal string value"

15 rdf:description + rdf:type There is still another way of representing the XML. This way makes it very clear that you are describing something, and it makes it very clear what the type (class) is of the thing you are describing: <rdf:description rdf:about=" xmlns=" <rdf:type rdf:resource=" <length>6300 kilometers</length> </rdf:description> This is read as: "This is a Description about the resource This resource is an instance of the River type (class). The resource has a length of 6300 kilometers, a startinglocation of western China's Qinghai-Tibet Plateau, and an endinglocation of the East China Sea." Note: this form of describing a resource is called the "long form". The form we have seen previously is an abbreviation of this long form. An RDF Parser interprets the abbreviated form as if it were this long form.

16 Alternative Alternatively we can use rdf:id rather than rdf:about, as shown here: <rdf:description rdf:id="yangtze" xmlns=" xml:base=" <rdf:type rdf:resource=" <length>6300 kilometers</length> </rdf:description>

17 Equivalent Representations! <River rdf:id="yangtze" xmlns=" xml:base=" <length>6300 kilometers</length> <River rdf:about=" xmlns=" <length>6300 kilometers</length> <rdf:description rdf:about=" xmlns=" <rdf:type rdf:resource=" <length>6300 kilometers</length> </rdf:description> Note: In the RDF literature the examples are typically shown in this form.

18 RDF Namespace ID about type resource Description

19 Terminology As you read the RDF literature you may see the following terminology: Subject: this term refers to the item that is playing the role of the resource. predicate: this term refers to the item that is playing the role of the property. Object: this term refers to the item that is playing the role of the value. Subject predicate Object Equivalent! Resource property Value

20 Modify the following XML document so that it is RDF-compliant: <River id="yangtze" xmlns=" <length>6300 kilometers</length> <Dam id="threegorges" xmlns=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> Yangtze2.xml

21 Note the two types (classes) River Dam Instance: Yangtze Properties: length startinglocation endinglocation Instance: ThreeGorges Properties: name width height cost

22 Dam - out of place Dam <River id="yangtze" xmlns=" <length>6300 kilometers</length> <Dam id="threegorges" xmlns=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> Types (classes) contain properties. Here we see the River type containing the properties - length, startinglocation, and endinglocation. It also shows River containing a type - Dam. Thus, there is a Resource that contains another Resource. This is inconsistent with RDF design pattern. (We are seeing one of the benefits of using the RDF format - to identify inconsistencies in an XML design.)

23 Property value must be a Literal or a Resource <length>6300 kilometers</length> property Value is a Resource property Value is a Literal <obstacle> <Dam id="threegorges" xmlns=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> </obstacle>

24 Modified XML (to make it consistent) <River id="yangtze" xmlns=" <length>6300 kilometers</length> <obstacle> <Dam id="threegorges" xmlns=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> </obstacle> Yangtze2,v2.xml "The Yangtze River has an obstacle that is the ThreeGorges Dam. The Dam has a name - The Three Gorges Dam. It has a width of 1.5 miles, a height of 610 feet, and a cost of $30 billion."

25 RDF Format <River rdf:id="yangtze" xmlns=" xml:base=" <length>6300 kilometers</length> <obstacle> <Dam rdf:id="threegorges" xmlns=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> </obstacle> Changed id to rdf:id Added the '#' symbol As always, the other representations using rdf:about and rdf:description are available.

26 RDF Model (graph)

27 Alternatively, suppose that someone has already created a document containing information about the Three Gorges Dam: <Dam rdf:id="threegorges" xmlns=" xml:base=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> Three-Gorges-Dam.rdf Then we can simply reference the Three Gorges Dam resource using rdf:resource, as shown here: <River rdf:id="yangtze" xmlns=" xml:base=" <length>6300 kilometers</length> <obstacle rdf:resource=" Yangtze.rdf

28 Anyone, Anywhere, Anytime Can Talk About a Resource In all of our examples we have provided a unique identifier to resources, e.g., Consequently, if another RDF document identifies the same resource then the data that it specifies gives additional data about that resource. An aggregator tool will be able to collect all data about a resource and present a consolidated set of data for the resource. That's powerful!

29 rdf:id versus rdf:about When should rdf:id be used? When should rdf:about be used? When you want to introduce a resource, and provide an initial set of information about a resource use rdf:id When you want to extend the information about a resource use rdf:about The RDF philosophy is akin to the Web philosophy. That is, anyone, anywhere, anytime can provide information about a resource.

30 XML <River id="yangtze" xmlns=" xmlns:uom=" <length uom:units="kilometers">6300</length> Yangtze4.xml RDF <River rdf:id="yangtze" xmlns=" xmlns:uom=" <length> <rdf:description> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </rdf:description> </length> Yangtze4.rdf

31 <River id="yangtze" xmlns=" xmlns:uom=" <length uom:units="kilometers">6300</length> Yangtze4.xml RDF does not allow attributes on the properties (except for special RDF attributes such as rdf:resource). So we need to make the uom:units attribute a child element. Your first instinct might be to modify length to have two child elements: <River id="yangtze" xmlns=" xmlns:uom=" <length> <value>6300</value> <uom:units>kilometers</uom:units> </length> However, now the length property has as its value two values. RDF only binary relations i.e., a single value for a property.

32 rdf:value length 6300 kilometers length has two values and kilometers. RDF provides a special property, rdf:value, to be used for specifying the "primary" value. In this example, 6300 is the primary value, and kilometers is a value which provides additional information about the primary value.

33 RDF Format An anonymous resource <River rdf:id="yangtze" xmlns=" xmlns:uom=" <length> <rdf:description> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </rdf:description> </length> Yangtze4.rdf Read this as: "The Yangtze River has a length whose value is a resource which has a value of 6300 and whose units is kilometers.

34 Advantage of anonymous resources <rdf:description> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </rdf:description> This is an anonymous resource. Its purpose is solely to provide a context for the two properties. Other RDF documents will have no need to amplify this resource. So, in this case, there is no reason for giving the resource an identifier. In this case it makes good sense to use an anonymous resource.

35 RDF Model (graph) Legend: An anonymous resource (also called a "blank node"). That is, a resource with no identifier. (Note: RDF Parsers will typically generate a unique identifier for anonymous resources, to distinguish one anonymous resource from another.)

36 rdf:parsetype="resource" If the value of a property is comprised of several values then one option is to create an anonymous resource, as we saw. RDF provides a shorthand, so that you don't need to create an rdf:description element, by using rdf:parsetype="resource", as shown here: <River rdf:id="yangtze" xmlns=" xmlns:uom=" <length rdf:parsetype="resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </length> Yangtze4,v2.rdf The meaning of this is identical to that shown on the previous slide.

37 Equivalent! <length> <rdf:description> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </rdf:description> </length> <length rdf:parsetype="resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </length>

38 RDF Format! <River rdf:id="yangtze" xmlns=" xmlns:uom=" xml:base=" <length rdf:parsetype="resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </length> <obstacle> <Dam rdf:id="threegorges" xmlns=" <name>the Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> </obstacle> Yangtze.rdf With relatively few changes the XML document is now usable by both XML tools and RDF tools!

39 Modify the following XML document so that it is also a valid RDF document: <River id="yangtze" xmlns=" xmlns:uom=" <length uom:units="kilometers">6300</length> <maxwidth uom:units="meters">175</maxwidth> <maxdepth uom:units="meters">55</maxdepth> Yangtze5.xml <River rdf:id="yangtze" xmlns=" xmlns:uom=" <length rdf:parsetype="resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </length> <maxwidth rdf:parsetype="resource"> <rdf:value>175</rdf:value> <uom:units>meters</uom:units></maxwidth> <maxdepth rdf:parsetype="resource"> <rdf:value>55</rdf:value> <uom:units>kilometers</uom:units> </maxdepth> Yangtze5.rdf This is one way of doing it. Now we will see a better way - using "typed literals". (See next slide)

40 Alternate RDF Format <River rdf:id="yangtze" xmlns=" <length rdf:datatype=" <maxwidth rdf:datatype=" <maxdepth rdf:datatype=" Yangtze5.rdf With rdf:datatype you can give a property's value a datatype label. The rdf:datatype value acts as a semantic label for the datatype of the value. This is called a typed literal. For this example there must be a namespace, which defines two datatypes - kilometer and meter. On the next slide is shown how to do this using XML Schemas.

41 Defining the kilometer and meter datatypes using XML Schemas <?xml version="1.0" encoding="utf-8"?> <schema xmlns:xsd=" targetnamespace=" <simpletype name="kilometer"> <restriction base="integer"> </restriction> </simpletype> <simpletype name="meter"> <restriction base="integer"> </restriction> </simpletype> </schema> uom.xsd

42 Another example using rdf:datatype <Person rdf:id="johnsmith" xmlns=" <age rdf:datatype=" </Person> In this example we are specifying that the value (30) of age is a nonnegativeinteger (which is defined in the XML Schema namespace).

43 The rdf:bag type (class) The rdf:bag type is used to represent an unordered collection.

44 Modify the following XML document so that it is also a valid RDF document: <Meeting id="xml-design-patterns" xmlns=" <attendees> <name>john Smith</name> <name>sally Jones</name> </attendees> </Meeting> DesignMeeting.xml <Meeting rdf:id="xml-design-pattern" xmlns=" <attendees> <rdf:bag> <name>john Smith</name> <name>sally Jones</name> </rdf:bag> </attendees> </Meeting> DesignMeeting.rdf rdf:bag makes it clear that this is an unordered collection of names.

45 The rdf:alt type (class) The rdf:alt type is used to represent a set of alternate properties.

46 Modify the following XML document so that it is also a valid RDF document: <Retailer id="barnesandnoble" xmlns=" <weblocation> <url> <url> </weblocation> </Retailer> BarnesAndNoble.xml <Retailer rdf:id="barnesandnoble" xmlns=" <weblocation> <rdf:alt> <url> <url> </rdf:alt> </weblocation> </Retailer> BarnesAndNoble.rdf rdf:alt makes it clear that the urls listed are alternates, i.e., choose one of them.

47 The rdf:seq type (class) The rdf:seq type is used to represent a sequence of properties.

48 Modify the following XML document so that it is also a valid RDF document: <ToDoList id="mondaymeetings" xmlns=" <activities> <activity1>meet with CEO at 10am</activity1> <activity2>luncheon at The Eatery</activity2> <activity3>flight at 3pm</activity3> </activities> </ToDoList> MyDaysActivities.xml <ToDoList rdf:id="mondaymeetings" xmlns=" <activities> <rdf:seq> <activity1>meet with CEO at 10am</activity1> <activity2>luncheon at The Eatery</activity2> <activity3>flight at 3pm</activity3> </rdf:seq> </activities> </ToDoList> MyDaysActivities.rdf rdf:seq makes it clear that the activities listed are to be done in the sequence listed.

49 rdf:li Property The property, rdf:li ("list item"), is provided by RDF for use with either rdf:bag, rdf:alt, or rdf:seq. The rdf:li property is provided for you to specify an item in a Bag/Alt/Seq. An RDF Parser will replace each rdf:li with rdf:_1, rdf:_2, rdf:_3, etc. The following slide recasts the previous examples using the rdf:li property.

50 <Retailer rdf:id="barnesandnoble" xmlns=" <weblocation> <rdf:alt> <rdf:li> <rdf:li> </rdf:alt> </weblocation> </Retailer> BarnesAndNoble.rdf <ToDoList rdf:id="mondaymeetings" xmlns=" <activities> <rdf:seq> <rdf:li>meet with CEO at 10am</rdf:li> <rdf:li>luncheon at The Eatery</rdf:li> <rdf:li>flight at 3pm</rdf:li> </rdf:seq> </activities> </ToDoList> MyDaysActivities.rdf <Meeting rdf:id="xml-design-pattern" xmlns=" <attendees> <rdf:bag> <rdf:li>john Smith</rdf:li> <rdf:li>sally Jones</rdf:li> </rdf:bag> </attendees> </Meeting> DesignMeeting.rdf

51 Dublin Core (dc:) The Dublin Core is a standard set of properties: Content Title Subject Description Language Relation Coverage Source Intellectual Property Creator Publisher Contributor Rights Instance Date Type Format Identifier Note: many people use these properties in their HTML today. For example: <META NAME="DC.Creator" CONTENT="John Smith">