DAMLS: Semantic Markup for Web Services

1
DAML-S Semantic Markup for Web Services
2
Content

• Introduction
• An Upper Service Ontology overivew- Service
  Profile- Service Model- Sevice Grounding
• Reasoning support
• Example
• Conclusions

3
What is DAML-S?

• Definition
• DAML-S is a DAMLOIL ontology of Web Services
  which goal is to represent Web programs and
  devices in a computer-interpretable manner.

4
Why DAMLOIL for Web Services

• Rich declarative service representationUDDI no
  capability description, limited to the name, a
  pointer and other link information
• The well-described semantic modelLack in WSDL
• Proved and implemented reasoning support

5
An Upper Ontology for Services

• DAML-S defines a set of classes and properties,
  specific to the description of services.
• The top of the DAML-S ontology is very general,
  i.e. it doesnt specify any particular subclasses
  of the root or even the conceptual basis for
  structuring the taxonomy.
• It is expected that the taxonomy will be
  structured according to functional and domain
  differences and market needs.

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An Upper Ontology for Services

• The class Service is the root of the DAML-S
  ontology.
• It is characterized by three important
  properties
• 1. A high-level description of a service and its
  provider.The class Service presents a
  ServiceProfile
• 2. A detalized description of the contol- and
  dataflow of the service.The class Service is
  describedBy a ServiceModel
• 3. A mapping from the (abstract) content of the
  service to some specific transmittable
  format(s).The class Service supports a
  ServiceGrounding

7
An Upper Ontology for Services

• Figure 1.

What it does
ServiceProfile
Resource
provides
presents
Service
supports
describedby
ServiceGrounding
ServiceModel
How it works
How to access it
8
Service Profile

• The class Service presents a ServiceProfile for
  describing the capabilities and parameters of the
  service.
• It answers the question
• What does the service require of agents, and
  provide for them?
• Informally, it specifies what the service does
  and is used by an agent to determine if the
  service meets its rough needs and satisfies
  constraints (security, locality, quality
  requirenments etc.).

9
Service Profile

• Service profiles consist of three types of
  information
• a description of the service and the service
  provider
• the functional behavior of the service
• several functional attributes (for automatic
  service selection)
• Implicitly, service profiles specify the intended
  purpose of the service, because they specify only
  those functional behaviors that are publicly
  provided.

10
Service Profile
11
Service Model

• The class Service is describedBy a ServiceModel,
  that specifies the workflow and possible
  execution paths of the service.
• It answers the question How does it work?
• It is used by an agent to
• perform more in-depth analysis of whether the
  service meets the agents needs
• compose service descriptions from multiple
  services to perform a specific task
• coordinate the activities of different agents

12
Process Model

• Web Services can be represented as processes,
  which details both the control structure and data
  flow structure of the services, i.e. the possible
  steps that are necessary to execute a service.
• The ProcessModel extends the ServiceModel and is
  used to describe services as processes.
• The Process Ontology consists of subclasses and
  properties of the ProcessModel class.

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The Process Ontology

• The basic class of the Process Ontology is the
  Process.
• Its sublcasses describe each process by
• any number of (possibly, conditional) inputs
• any number of (possibly, conditional) outputs
• any number of preconditions, which must hold in
  order for the process to be invoked
• any number of (possibly, conditional) side
  effects
• any number of participants (subprocess)

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Types of the process in DAML-S

• Atomic processes directly invokable (by an
  agent), have no subprocesses, executed in a
  single step.
• Composite processes consist of other
  (non-composite or composite) processes.They have
  a composedOf property, by which the control
  structure of the process is indicated, using a
  ControlConstruct subclasses (see table ).
• Simple processes abstract concepts, used to
  provide a view of some atomic process, or a
  simplified representation of some composite
  process (i.e., the black box view of a
  collapsed composite process).

15
Control Constructs of Processes
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Service Grounding

• The class Service supports a ServiceGrounding,
  that describes a mapping from an abstract
  (ServiceProfile and ServiceModel) to a concrete
  specification of the service description
  elements, that are required for interacting with
  the service, i.e. the inputs and outputs of
  atomic processes.
• The central function of a DAML-S grounding is to
  show how the (abstract) inputs and outputs of an
  atomic process are to be realized concretely as
  messages, which carry those inputs and outputs in
  some specific transmittable format (e.g. RPC,
  CORBA, Java RMI, HTTP etc.).

17
Reasoning in DAML-S

• Service requests are constructed as partial
  service descriptions.
• Requests are then evaluated against the
  advertised service taxonomy using subsumption
  (classification).
• Matches are generally recognized whenever the
  service advertised is subsumed by (is a
  particular case of) the service description
  requested.
• Note Advertisements and requests can differ
  sharply, in level of detail and in the level of
  abstraction of the terms used.

18
Example

• To illustrate the main concepts, an example of a
  fictious book-buying service, provided by Congo
  Inc., has been developed.
• This service is, in fact, a collection of smaller
  programs, some of which are used in this
  presentation.
• The whole example can be found at
• http//www.daml.org/services/daml-s/2001/05/Congo.
  daml

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Example an atomic process

• The LocateBook program takes as input the name of
  a book and returns a description of the book and
  its price (if the book is in catalogue).
• ltdamlClass rdfIDLocateBookgt
• ltrdfssubClassOf rdfresoucehttp//www.daml.or
  g/services/daml-s/2001/10/Process.damlAtomicProce
  ss /gt
• ltrdfssubClassOfgt
• ltdamlRestriction damlcardinality1gt
• ltdamlonProperty rdfresourcebookName/gt
• lt/rdfssubClassOfgt
• lt/damlClassgt
• ltrdfProperty rdfIDbookNamegt
• ltrdfssubPropertyOf rdfresourcehttp//www.dam
  l.org/services/daml-s/2001/10/Process.damlinput
  /gt
• ltrdfsdomain rdfresourceLocateBook/gt
• ltrdfsrange rdfresourcehttp//www.w3.org/2000
  /10/XMLSchemastring"/gt
• lt/rdfPropertygt

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Example an atomic process

• ltrdfProperty rdfIDbookDescriptiongt
• ltrdfssubPropertyOf rdfresourcehttp//www.dam
  l.org/services/daml-s/2001/10/Process.damlconditi
  onalOutput /gt
• ltrdfsdomain rdfresourceLocateBook/gt
• ltrdfsrange rdfresourceInCatalogueBookDescrip
  tion/gt
• lt/rdfPropertygt
• ltdamlClass rdfIDInCatalogueBookDescriptiongt
• ltrdfssubClassOf rdfresoucehttp//www.daml.or
  g/services/daml-s/2001/10/Process.damlConditional
  Output /gt
• lt/rdfssubClassOfgt
• lt/damlClassgt

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Example an atomic process

• ltrdfProperty rdfIDcondInCatalogueBookDescripti
  ongt
• ltrdfssubPropertyOf rdfresourcehttp//www.dam
  l.org/services/daml-s/2001/10/Process.damlcoCondi
  tion /gt
• ltrdfsdomain rdfresourceInCatalogueBookDescr
  iption/gt
• ltrdfsrange rdfresourceInCatalogueBook/gt
• lt/rdfPropertygt
• ltrdfProperty rdfIDoutInCatalogueBookDescriptio
  ngt
• ltrdfssubPropertyOf rdfresourcehttp//www.dam
  l.org/services/daml-s/2001/10/Process.damlcoOutpu
  t /gt
• ltrdfsdomain rdfresourceInCatalogueBookDescr
  iption/gt
• ltrdfsrange rdfresourceTextBookDescription/
  gt
• lt/rdfPropertygt
• ltdamlClass rdfIDTextBookDescriptiongt
• ltrdfssubClassOf rdfresource
  http//www.daml.org/2001/03/damloilThing /gt
• lt/damlClassgt

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Example a composite process

• With a description of each of the atomic
  programs/processes in hand, it possible then to
  describe compositions of these programs that
  provide specific services.
• The DAML-S composite process is built recursively
  in a top-down manner. Each CompositeProcess is
  composedOf a ControlStructure, which may be a
  Sequence, If-then-else, etc. Each such
  ControlConstruct, in turn, has a components
  property, which specify the classes of the
  subcomponents.

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Example a composite process

• In the Congo example, CongoBuy was described in
  terms of two main steps locating the book, and
  then buying it.
• ExpandedCongoBy is the name for the sequence of
  the atomic process LocateBook, followed by the
  composite process CongoBuyBook.
• Other restrictions (on inputs, outputs,
  preconditions and effects) can also be specified.

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Example a composite process

• ltdamlClass rdfIDExpandedCongoBuygt
• ltrdfssubClassOf rdfresoucehttp//www.daml.or
  g/services/daml-s/2001/10/Process.damlCompositePr
  ocess /gt
• ltrdfssubClassOfgt
• ltdamlRestrictiongt
• ltdamlonProperty rdfresourcehttp//www.daml.
  org/services/daml-s/2001/10/Process.damlcomposedO
  f /gt
• ltdamltoClassgt
• ltdamlClassgt
• ltdamlintersectionOf rdfparseTypedamlcolle
  ctiongt
• ltdamlClass rdfaboutprocessSequence/gt
• ltdamlRestrictiongt
• ltdamlonProperty rdfresource
  processcomponents/gt
• ltdamltoClassgt
• ltdamllistOfInstanceOf
  rdfparseTypedamlcollectiongt
• ltdamlClass rdfaboutLocateBook/gt
• ltdamlClass rdfaboutCongoBuyBook/gt
• lt/damllistOfInstanceOf
  rdfparseTypedamlcollectiongt
• lt/damlClassgt
• lt/damltoClassgt
• lt/damlRestrictiongt

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Example a simple process

• ltdamlClass rdfID CongoBuygt
• ltrdfssubClassOf rdfresouceprocessSimpleP
  rocess /gt
• lt/damlClassgt
• ltdamlClass rdfaboutCongoBuygt
• ltrdfssubClassOfgt
• ltdamlRestrictiongt
• ltdamlonProperty rdfresourceprocess
  expand/gt
• ltdamltoClass rdfresource
  ExpandedCongoBuy/gt
• lt/damlRestrictiongt
• lt/rdfssubClassOfgt
• lt/damlClassgt

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Conclusions

• DAML-S is an upper ontology for describing
  Web-Services, written in DAMLOIL.
• By providing a rich declarative representation
  and an efficient reasoning support, DAML-S
  addresses the objective of making Web Services
  computer-interpretable and, hence, enables their
  automatic discovery, invocation, verification,
  composition and interoperation as well as
  execution monitoring.