1 introduction to the semantic web and metadata frameworks payam barnaghi institute for...
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Introduction to the Semantic Web and metadata frameworks
Payam BarnaghiInstitute for Communication Systems (ICS)Faculty of Engineering and Physical Sciences University of SurreySpring 2015
Lecture 6: Mobile Applications and Web Services module
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The Semantic Web
“The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in co-operation.“
[Berners-Lee et al, 2001]
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Syntactic Web
− The syntactic Web content is suitable for human use.− Typical uses of the Web today are information seeking,
publishing, and using, searching for people, documents, products, shopping, reviewing catalogues, etc.
− Dynamic pages generated based on information from databases but without original information structure found in databases.
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Searching for the information on the Web
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Limitations of the syntactic Web search
− The Web search results are high recall, low precision.
− Results are highly sensitive to vocabulary.− Results are single Web pages. − Most of the publishing contents are not structured
to allow logical reasoning and query answering.
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Why do I need to learn about semantic web and metadata frameworks?
− Mobile technologies are growing fast and are becoming diverse and in result:
− We have multi-modal and heterogeneous data and services
− These data and services could have different qualities, provenance, interfaces,… that need to be captured and described.
− This information should be machine-readable and should be interoperable across different platforms.
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What I am going to learn
− Key concepts and technologies for describing and representing semantics and metadata
− How semantic technologies can improve the access to the data/service and enhance the interoperability
− Resource description framework (RDF) and representation formats.
− Designing and representing RDF models.
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So, let’s see what’s the main problem that semantic web tries to solve.
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Big Data
− "Big data" is a term applied to data sets whose size is beyond the ability of commonly used software tools to capture, manage, and process the data within a tolerable elapsed time. Big data sizes are a constantly moving target, as of 2012 ranging from a few dozen terabytes to many petabytes of data in a single data set.” (wikipedia)
− Every day, we create 2.5 quintillion bytes of data — so much that 90% of the data in the world today has been created in the last two years alone. (source IBM)
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Data on the Web
Does he have any knowledge in AI?
Who are his colleagues working in
similar areas?
I am looking for a potential supervisor
in WoT, who works on the topic at Uni
Surrey?
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What machines see…
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Links on the syntactic Web
In HTML: <a href=http://www.surrey.ac.uk ….>In real life semantics: link to where I work
href
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i.e. the Syntactic Web is…
− A place where − computers do the presentation (easy) and − people do the linking and interpreting (hard).
− Why not get computers to do more of the hard work?
Source: [Carole Goble, 03]
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Some have already started…
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Cosm- Sensor Data on the Web
Tags
Data formats
Location
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Mobile Applications and Services
- Various types of data, heterogeneous interfaces, applications…- Interoperability is a problem, interpretation of data/services- Discovery of information, automated interactions….
-We need more structured and/or machine-interpretable of data/service descriptions
Image courtesy: Economist.com
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Machine-accessible Content
− The main obstacle to provide better support to Web users is that, at present , the meaning of Web content is not machine accessible.
− Although there are tools to retrieve texts, but when it comes to interpreting sentence and extracting useful information for the user, the capabilities of current software are still very limited.
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Distinguishing the meaning
− It is simply difficult for machines to distinguish the meaning of:
I am a philosopher.from
I am a philosopher, you may think. Well,…
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Limitations of the syntactic Web
The Web interactions are mostly focus on Machine-to-Human,
and Machine-to-Machine activities are well supported.
With growing size of information, finding, processing and accessing the information is becoming more and more difficult.
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XML
<H1>Mobile Applications and Web Services</H1><UL>
<LI>Module Code: EEEM042<LI>Level: MSc
</UL>
<H1>Mobile Applications and Web Services</H1><UL>
<LI>Module Code: EEEM042<LI>Level: MSc
</UL>
HTML:
<module><title>Mobile Applications and Web Services</title><code> EEEM042 </code><level>MSc</level>
</module>
<module><title>Mobile Applications and Web Services</title><code> EEEM042 </code><level>MSc</level>
</module>
XML:
User definable and domain specific markup
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XML: Document = labeled tree
module
lecturertitle students
name weblink
<module date=“...”><title>...</title><lecturer>
<name>...</name><weblink>...</
weblink></lecturer><students>...</students>
</module>
=
DTD: describe the grammar and structure of permissible XML trees
node = label + contents
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But What about this?
<module><title>Mobile Applications and Web Services</title><code> EEEM042 </code><level>MSc</level>
</module>
<module><title>Mobile Applications and Web Services</title><code> EEEM042 </code><level>MSc</level>
</module>
<μονάδα><τίτλος>Mobile Applications and Web Services</τίτλος><κώδικας> EEEM042 </κώδικας ><επίπεδο>MSc</επίπεδο>
</μονάδα>
<μονάδα><τίτλος>Mobile Applications and Web Services</τίτλος><κώδικας> EEEM042 </κώδικας ><επίπεδο>MSc</επίπεδο>
</μονάδα>
<módulo><título>Mobile Applications and Web Services</título><código> EEEM042 </código><nivel>MSc</nivel>
</módulo>
<módulo><título>Mobile Applications and Web Services</título><código> EEEM042 </código><nivel>MSc</nivel>
</módulo>
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XML
− Meaning of XML-Documents is intuitively clear− due to "semantic" Mark-Up− tags are domain-terms
− But, computers do not have intuition− tag-names do not provide semantics for machines.
− DTDs or XML Schema specify the structure of documents, not the meaning of the document contents
− XML lacks a semantic model− has only a "surface model”, i.e. tree
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XML: limitations for semantic markup
− XML representation makes no commitment on:− Domain specific ontological vocabulary
− Which words shall we use to describe a given set of concepts?
− Ontological modelling primitives− How can we combine these concepts, e.g. “car is a-kind-of (subclass-of) vehicle”
requires pre-arranged agreement on vocabulary and primitives
Only feasible for closed collaboration agents in a small & stable community pages on a small & stable intranet
.. not for sharable Web-resources
Source: [John Davies, BT, 03]
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XML is a first step
− Semantic markup− HTML layout− XML content
− Metadata− within documents, not across documents− prescriptive, not descriptive− No commitment on vocabulary and modelling primitives
− RDF is the next step
Source: [John Davies, BT, 03]
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Resource Description Framework (RDF)
− A W3C standard− Relationships between documents− Consisting of triples or sentences:
− <subject, property, object>
− <“Mozart”, composed, “The Magic Flute” >− RDFS extends RDF with standard “ontology vocabulary”:
− Class, Property− Type, subClassOf− domain, range
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RDF for semantic annotation
− RDF provides metadata about Web resources,− Object -> Attribute-> Value triples,− It has an XML syntax,− Chained triples form a graph.
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RDF: Basic Ideas
− Resources− Every resource has a URI (Universal Resource Identifier)− A URI can be a URL (a web address) or a some other kind of
identifier;− An identifier does not necessarily enable access to a resources− We can think of a resources as an object that we want to
describe it.− Books− Person− Places, etc.
http://mydomain.com/myaccount/myhouse/
http://personal.ee.surrey.ac.uk/Personal/P.Barnaghi/
http://www.amazon.com/....
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RDF: Basic Ideas
− Properties− Properties are special kind of resources;− Properties describe relations between resources.− For example: “written by”, “composed by”, “title”, “topic”,
etc.− Properties in RDF are also identified by URIs.− This provides a global, unique naming scheme.
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RDF: Basic Ideas
− Statements− A statement is an object-attribute-value triple.− It consists of a resources, a property, and a value.
http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10140
publishedBy#MIT Press
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RDF: Example
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RDF Schema: Basic Ideas
− RDF is a universal language that enables users to describe their own vocabularies.
− But, RDF does not make assumption about any particular domain.
− It is up to user to define this in RDF schema.
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What does RDF Schema add?
• Defines vocabulary for RDF• Organizes this vocabulary in a typed
hierarchy• Class, subClassOf, type• Property, subPropertyOf• domain, range
AlanTom
Staff
Lecturer Research Assistant
subClassOfsubClassOf
type
supervisedBydomain range
type
supervisedBy
Schema(RDFS)
Data(RDF)
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Creating RDF
− An RDF Resource is anything that can have a URI, − For example:
− "http://en.wikipedia.org/wiki/University_of_Surrey"
− An RDF Property is a “Resource” that has a name, − For example:
− “hasLocation" or "hasLogo"
− A Property value is the value of a Property, which can be another resource.− For example:
− http://en.wikipedia.org/wiki/Guildford− http://en.wikipedia.org/wiki/File:University_of_Surrey_Logo.svg
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Creating an RDF document
− First include the RDF Document Root Tag
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <!– RDF body will be added here --> </rdf:RDF>
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Creating an RDF document
− Next add the statement(s)− An RDF document can include more than one statement.− An RDF statement begins with an rdf:Description tag.− In XML serialisation of RDF, a statement can contain one or
more statements about the same subject:
<rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#>
<rdf:Description rdf:about=" http://en.wikipedia.org/wiki/University_of_Surrey">
<!– Statement descriptions will be included here --> </rdf:Description>
</rdf:RDF>
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Creating an RDF document
− Adding predicates
<rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#xmlns:uni="http://mynamespace/uni-features#">
<rdf:Description rdf:about=" http://en.wikipedia.org/wiki/University_of_Surrey">
<uni:established>1966</uni:established> </rdf:Description>
</rdf:RDF>
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Creating an RDF document
− An RDF statement can have a literal value or it can be refer to the subject (ID) of another statement.
<rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#xmlns:uni="http://mynamespace/uni-features#">
<rdf:Description rdf:about=" http://en.wikipedia.org/wiki/University_of_Surrey">
<uni:established>1966</uni:established>
<uni:location rdf:resource=“http://en.wikipedia.org/wiki/Guildford” />
</rdf:Description>
</rdf:RDF>
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Object property
− A subject in an RDF document can be referenced as an object of a property in another RDF statement similar to the previous example.
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XML is not the only way to describe RDF
− Turtle - Terse RDF Triple Language− Turtle is a textual syntax for RDF.− It allows RDF graphs to be completely written in a
compact and natural text form, with abbreviations for common usage patterns and data types.
− Turtle provides levels of compatibility with the existing N-Triples and Notation 3 (N3) formats.
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N-Triples
− N-Triples is a line-based, plain text format for encoding an RDF graph. It was designed to be a fixed subset of N3.
− N-Triples can be used to define the correspondence between RDF/XML and the RDF abstract syntax. RDF/XML [RDF-SYNTAX] (and also recently Turtle) are the W3C recommended syntax for applications to exchange RDF information.
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Turtle
− URIs may also be abbreviated by using Turtle's @prefix directive that allows declaring a short prefix name for a long prefix of repeated URIs.
− This is useful for many RDF vocabularies that are all defined in nearby namespace URIs, possibly using XML's namespace mechanism that works in a similar fashion.
− For example, where @prefix doc: <http://example.org/ns#> is defined, any mention of a URI later in the document may use a qualified name that starts doc: to stand for the longer URI.
− In the following, the qualified name doc:Document is a shorthand for the URI http://example.org/ns#Document.
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Conclusions about RDF(S)
− RDF is a step forward from plain XML:− It provides (limited) ontological commitment to
modeling primitives− It enables to define a vocabulary− However, there are no precisely described meaning− Next week will be describing OWL and concept of
ontologies.
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Exercise 1
− Write an RDF statement for this diagram.
John Smith
http://somesite/JohnSmit
Vcard:FN
You can start with: <rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#' xmlns:vcard='http://www.w3.org/2001/vcard-rdf/3.0#' > ….
</rdf:RDF>
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Validating your RDF
− You can validate your RDF using W3C RDF validate:− http://www.w3.org/RDF/Validator/
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Exercise 2
− Draw a graph demonstrating this RDF document:
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Exercise 3
− Write an XML/RDF description for the following N3 RDF code.
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Questions?