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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

GloServ: Global Service Discovery Architecture

Knarig Arabshian and Henning Schulzrinne

IRT internal talk

April 8, 2004

  • Motivation
  • Background
    • RDF and RQL
  • Architecture
    • Hierarchy, registration, query
  • Related work
  • Conclusions and future work


what is service discovery
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 ...


why global services
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


what are the challenges
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 –
      • Service based –


service description 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)


more rdf 2
More RDF [2]

(subject, predicate, object)

doc , title, My resume

doc, editor, <>

<>, homePage, http://…

<>, fullName, Alice Cueba



My resume




Alice Cueba


more rdf 3
More RDF [3]

My resume

Alice Cueba


rdf schema
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


rdf schema 2

A dining establishment



RDF schema [2]


query in rdf
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


query in rdf 2
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


architecture hierarchy
Architecture: Hierarchy









determination of service hierarchy
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






1)Present user with service hierarchy

2) Choose hierarchy level to register to


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



user query
User Query


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



generating uri to contact correct authoritative server
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


generating uri to contact correct authoritative server1
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:
    • Generate URI:
    • If this URI doesn’t exist, try the sibling location
    • May also try just the service URI itself in case it is not a location-based service (gloserv:restaurant.service)


query within authoritative server
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


related work
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.


related work1
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.


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.


conclusion and future work
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