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GloServ: Global Service Discovery Architecture

GloServ: Global Service Discovery Architecture. Knarig Arabshian and Henning Schulzrinne IRT internal talk April 8, 2004. Agenda. Motivation Background RDF and RQL Architecture Hierarchy, registration, query Related work Conclusions and future work. What is service discovery?.

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GloServ: Global Service Discovery Architecture

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  1. GloServ: Global Service Discovery Architecture Knarig Arabshian and Henning Schulzrinne IRT internal talk April 8, 2004

  2. Agenda • Motivation • Background • RDF and RQL • Architecture • Hierarchy, registration, query • Related work • Conclusions and future work GloServ/Knarig

  3. What is service discovery? • Where is “foo”? Who is responsible for “bar”? • What Italian restaurants are near Columbia University? • Events + services • Can be location-based …there is a classical music concert at 7pm across the street, near your hotel ... GloServ/Knarig

  4. Why global services? • Ubiquitous computing is becoming prevalent in today’s society • Traveler visiting a new city wants to know all classical music events. • Doctor visiting a hospital wants to know medical services in this hospital. • Visitor in starbucks wants to know if it offers local internet TV. Service discovery should be global GloServ/Knarig

  5. What are the challenges? • Service description and querying • Too specific: does not extend to a new service • Too broad: difficult to search or find • Semantically describe services • Global scale • Flat: does not scale • Hierarchy: like DNS • Location based – restaurant.service.newyork.ny.us • Service based – newyork.ny.us.service.restaurant GloServ/Knarig

  6. <?xml version=“1.0”?> <RDF> <Restaurant about=“http://…/PatsPizza.html”> <Cuisine>Italian</Cuisine> <Rating>6</Rating> </Restaurant> </RDF> Resource Description Framework (RDF) XML-based by W3C Originally designed to represent metadata for web resources Semantically defines web resources Identify things using URI Describe using properties and property values Service description (RDF) GloServ/Knarig

  7. More RDF [2] (subject, predicate, object) doc , title, My resume doc, editor, <> <>, homePage, http://… <>, fullName, Alice Cueba http://www.home.com/doc editor title My resume fullName homePage http://www/~alice Alice Cueba GloServ/Knarig

  8. More RDF [3] <?xml version=“1.0”> <rdf:RDF xmlns:rdf=“…” …> <rdf:Description rdf:about=“http://www.home.com/doc”> <dc:title>My resume</dc:title> <a:editor rdf:nodeID=“editorInfo”/> </rdf:Description> <rdf:Description rdf:nodeID=“editorInfo”> <a:fullName>Alice Cueba</a:fullName> <a:homePage rdf:resource=“http://www/~alice”/> </rdf:Description> </rdf:RDF> GloServ/Knarig

  9. RDF schema • Vocabulary description language that provides a type system for RDF. • Classes are similar to object-oriented classes • Properties are similar to members within a class • (Subject, predicate, object) => (Class, property, property value) • Example: • Restaurant, rating, 6 • Restaurant, cuisine, Italian • Rating = (domain=>Restaurant, range=>literal) • Classproperty : can be many-to-many • Classes can have subclasses, Properties can have subproperties GloServ/Knarig

  10. <RDF …> <Class ID=“Restaurant”> <Comment>A dining establishment </Comment> <label>Restaurant</label> </Class> <Property ID=“Rating”> <domain resource=“#Restaurant”> <range resource=“#Literal”> </Property> <Property ID=“Cuisine”> <domain resource=“#Restaurant”> <range resource=“#Literal”> </Property> </RDF> <RDF …> <Restaurant about=“http://…/PatsPizza.html”> <Cuisine>Italian</Cuisine> <Rating>6</Rating> </Restaurant> </RDF> RDF schema [2] GloServ/Knarig

  11. Query in RDF • Different querying languages for RDF • RDF data query language (RDQL) • RDF query language (RQL) • Chose RQL • Allows schema query (why needed?) Select Y from {X} rating {Y} Where X=“http://…/PatsPizza” Result: Y=6 Find me the rating of pat’s pizza GloServ/Knarig

  12. Query in RDF [2] Querying the properties that belong to a particular domain select @X from Property{@X} where @X in domain( Restaurant ) =>Result: @X = Rating, Cuisine Querying subclasses of a particular class select $X from Class{$X} where $X in subClassOf( Event ) =>Result: $X = Classical, Medical, Emergency GloServ/Knarig

  13. Architecture: Hierarchy event service restaurant.service medical.event concert.event GloServ/Knarig jazz.concert.event classical.concert.event

  14. Determination of Service Hierarchy • The GloServ architecture is similar to DNS • root name servers • authoritative name servers that manage the information of services. • Separate classification system similar to North American Industry Classification System (NAICS) • classifies the hierarchy of services • establishes RDF schemas that describe each type of service • The service categorization is similar to yellow pages directory. • Authority such as ICANN delegates the top level services GloServ/Knarig

  15. Registration Service Agent Operator 1)Present user with service hierarchy 2) Choose hierarchy level to register to gloserv:registrar 4)Create form (according to the meta data) for user to fill out 3) Generate URI and contact correct server to obtain meta data for GUI 5)Verify service agent and store RDF document in server restaurant.service GloServ/Knarig

  16. User Query User 1)Present user with services offered 2) Choose service to query to Local user agent 4)Create query form (according to the meta data) for user to fill out 3) Generate URI and contact correct server to obtain meta data for GUI 5)Formulate RQL query and obtain list of services restaurant.service GloServ/Knarig

  17. Generating URI to contact correct Authoritative Server • Service Level • User chooses the level of the hierarchy it wants to either register to or query to • Registrar and Local User Agent: • Concatenate the service hierarchy into a URI: service->restaurant will evaluate to gloserv:restaurant.service GloServ/Knarig

  18. Generating URI to contact correct Authoritative Server • Location Level • Find out the nearest location-based servers by querying its cached RDF store of its location hierarchy: new_york.ny.us • Generate URI: gloserv:restaurant.service.new_york.ny.us • If this URI doesn’t exist, try the sibling location gloserv:restaurant.service.brooklyn.ny.us • May also try just the service URI itself in case it is not a location-based service (gloserv:restaurant.service) GloServ/Knarig

  19. Query within Authoritative Server • restaurant.service authoritative server will execute RQL query on its RDF store and return matches • User may also add additional text to search for • This evaluates to a heuristic that searches for (subject, predicate, objects) that match the text • May not be as accurate • Gives user opportunity to choose from a broader list of services GloServ/Knarig

  20. Related Work • SLP (Service Location protocol) • User Agents (UA) perform service discovery on behalf of a client • Service Agents (SA) which advertise location and characteristics of the service on behalf of the service • Directory Agents (DA), records available services and also responds to service requests from UAs (optional). • Two modes of operation • DA exists: UAs learn of services available by unicasting their requests to the DA. • DA doesn’t exist: UAs repeatedly multicast messages to Sas that responds to the UAs via unicast. GloServ/Knarig

  21. Related Work • JINI • Built on top of the Java object and RMI system. • Service registries, similar to SLP’s DAs • The Java class hierarchy defines services and their attributes. • UPnP • Doesn’t have a central service registry • Services multicast their announcements to control points that are listening • Control points can also multicast discovery messages and search for devices within the system. • XML describes the services in greater detail. GloServ/Knarig

  22. Differences/Similarities • Scaling • SLP and Jini can cover small networks as well as larger enterprise networks • UPnP appropriate for home or small office networks. • Querying • Simple text-based attribute-value query languages for SLP and Jini • UPnP provides more descriptive queries through XML. • Main Drawbacks • do not cover a wide area network that spans the whole Internet • SLP, Jini provide simpler querying mechanism which do not give enough flexibility to the system. GloServ/Knarig

  23. Conclusion and Future Work • GloServ is a global service discovery architecture • Uses RDF/RQL to describe and query for services • Hierarchical definition of services • Building a prototype implementation of GloServ GloServ/Knarig

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