Transcript Introduction to Grid Computing, Lecture 2.2 - VL

WS-Resource Framework
Adam Belloum
Computer Architecture & Parallel Systems group
University of Amsterdam
[email protected]
Grid and Web Services: Convergence?
Grid
Started
far apart
in apps
& tech
Have been
converging
?
Web
However, despite enthusiasm for OGSI, adoption
within Web community turned out to be problematic
“WS-Resource Framework: Globus Alliance Perspectives” I. Foster
Grid and Web Services:
Convergence: Yes!
Grid
Started
far apart
in apps
& tech
Have been
converging
WSRF
Web
The definition of WSRF means that Grid and Web
communities can move forward on a common base
“WS-Resource Framework: Globus Alliance Perspectives” I. Foster
Web Service and State
• Web service interfaces frequently provide a user with the ability to
access and manipulate state
– Message exchanges that Web services implement are frequently intended
to enable access to stateful resources.
• However, the notion of stateful resources acted upon by the Web
service implementation is not explicit in the interface definition.
Web Service and State
• It is desirable to define Web service conventions to enable:
– the discovery of, introspection on, and interaction with
stateful resources in standard and interoperable ways.
• WS-Resource is approach to modeling state in a Web
services context
Web Service and State
• A WS-Resource is defined as the composition of a Web service
and a S-Resource
– Expressed as an association of an XML document with defined type
with a Web services portType
– Addressed and accessed according to the implied resource pattern,
• a conventional use of WS-Addressing endpoint references
• In the implied resource pattern, a S-Resource identifier is
encapsulated in an endpoint reference
• to identify the S-Resource to be used in the execution of a Web service
message exchange.
WS-Resource Framework
• WS-Resource framework allows WS-Resources to be
– declared, created, accessed, monitored for change, and
destroyed via conventional Web services mechanisms,
• but
– does not require that the WS component of the WS-Resource
to be implemented as a stateful message processor.
The five specification composing
the WSRF
How these proposals relates to
other Web services standards:
Service
Composition
Quality of
Experience
(QoX)
WS-Service Group
BPEL4WS
WS-Notification
WS-Reliable Messaging
WS-Security
WS-Transaction
WS-Resource Lifetime
WS-Resource Properties
WS-Base Faults
Description
WSDL
XSD
Messaging
XML
SOAP
Transports HTTP/HTTPS
WS-Policy
WS-Metadata Exchange
WS-Addressing WS-Renewable References
SMTP
RMI / IIOP
JMS
Renewable References
• The WS-RenewableReferences work defines mechanisms that can
be used to renew an endpoint reference that has become invalid.
• These mechanisms can be applied to any endpoint reference, but
are particularly useful
– For endpoint reference that refers to a WS-Resource,
– as it can provide a persistent and stable reference to the WS-Resource
that can allow the same state to be accessed repeatedly over time.
Renewable References
• A WS-Addressing endpoint reference may contain
– not only addressing
– policy information concerning interactions with the service.
• Typically, endpoint references are constructed by an authoritative source of the
addressing and policy information.
• An endpoint reference made available to a client represents a copy
of that information
– at some point, become incoherent due to changes introduced by the
authoritative source that effects the endpoint location and/or the policy
Service Groups
• The WS-ServiceGroup specification defines a means of
representing and managing heterogeneous by-reference
collections of Web services.
– organize collections of WS-Resources, for example to build
registries
– build services that can perform collective operations on a
collection of WS-Resources.
Service Groups
• The ServiceGroup specification
express ServiceGroup:
– membership rules,
– Membership constraints
– classifications.
•
using the resource property
model from WSResourceProperties
•
as a collection of members that
meet the constraints of the
group as expressed through
resource properties
• Groups can be defined.
Base Faults
• The WS-BaseFaults specification defines a base fault type for
use when returning faults in a Web services message
exchange.
• Used by all of the other WS-Resource framework specifications
to bring consistency to the faults returned by the operations
including
– consistent reporting of faults relating to WS-Resource definition
and use.
Notification
• WS-Notification, defines a general, topic based WS system for
(pub/sub) interactions that builds on the WS-Resource framework.
• From the perspective of WS-Notification
– WS-Resource framework provides useful building blocks for
representing and structuring notifications.
• From the perspective of the WS-Resource framework,
– WS-Notification specifications extends WS-Resources by allowing
requestors to ask to be asynchronously notified of changes to resource
property value
Modeling Stateful Resources
with Web Services
Possible association
between State and Services
• A stateless service implements
– message exchanges with no access or use of information not
contained in the input message
• A conversational service implements
– a series of operations such that the result of one operation depends on
a prior operation and/or prepares for a subsequent operation
• A service that acts upon stateful resources
– access to, or manipulates a set of logical stateful resources based on
messages it sends and receives.
Stateless Implementations,
Stateful Interfaces
• A Service that acts upon stateful resources may be
described “stateless”
– if it delegates responsibility for the management of the state
to another component.
• The service is responsible for the state of the resource
between message exchanges
A consequence of
statelessness
• Any dynamic state needed for a given message-exchange
execution must be:
– provided explicitly within the request message, whether
• directly by-value
• indirectly by-reference maintained implicitly within other system
components with which the WS can interact.
Modeling State in Web
Services (WS-Resource)
• WS-Resource is composed of a Web service and a S-Resource
• S-Resource is used in the execution of Web service message
exchanges
• WS-Resources can be created and destroyed
• S-Resource is associated with the interface of a WS to enable:
well-formed queries against the state of a WS-Resource
Modeling State: Stateful
Resources
• A S-Resource is defined as having:
– specific set of state data expressible in XML format
– a well-defined lifecycle known to, and acted upon, by one or more
Web services.
How stateful resource is
referred to by Web services?
The implied resource pattern refers to the mechanisms used to
associate
– a S-Resource
– with the execution of message exchanges implemented by a
Web Service.
The Implied Resource Pattern
• Implied is used because the S-Resource associated with a
message exchange is treated as implicit input for the execution of
the message request.
– The Association of WS and S-Resource is either static or a dynamic.
• Static if the association is made when the WS is deployed.
• Dynamic if the association is made at time of message exchange
(S-Resource is encapsulated in the WS-Addressing endpoint
reference).
•
Pattern indicates that the relationship between WS and Sresources is
– codified by a set of conventions on existing WS technologies, in
particular XML, WSDL, and WS-Addressing.
WS-Addressing
• WS-Addressing standardizes
– The endpoint reference used to represent the address of a WS.
– endpoint contain metadata associated with the WS
• service description information
• reference properties
• A WS-Addressing endpoint reference is an XML serialization of a
network-wide pointer to a WS
WS-Resource and WSAddressing
•
SW (2) returns an Endpoint
reference to the requestor
•
“C” is S-resource created
•
SW (2) represents an explicit
WS-Resource factory.
•
The endpoint reference (3)
contains
–
Wsa:Address (4)
•
•
–
refers to the network
transport-specific address of
the WS (URL).
same address that would
appear within a port element
in a WSDL of the WS
wsa:ReferencePropertie
•
contain an XML serialization
of a S-Resource identifier.
WS-Resource and WSAddressing
• S-Resource identifier
– is meaningful only to the SW,
– used by the WS in an
implementation-specific to
identify the WS-Resource related
S-Resource needed for the
execution.
– should not be examined or
interpreted by the service
requestor’s applications
– Is represented using a servicespecific XML element by XML
serialization of the S-Resource
WS-Resource and WSAddressing
• S-Resource identifier
– must identify a unique SResource to be used the
execution of the request
message.
– the scope of the S-Resource
identifier must be unique
within the scope of the WS.
– multiple identifiers within the
scope of a WS may refer to
the same WS-Resource.
WS-Resource-qualified
endpoint reference
• the endpoint reference
represents a pointer to the
WS-Resource
• service requestor
– must understand that the
endpoint reference refers
to a WS-Resource.
– must recognize that the
endpoint reference is a
WS-Resource qualified
endpoint reference.
WS-Resource-qualified
endpoint reference
•
requestor use the endpoint
reference (1) to send
messages (2) to the
identified SW(3)
•
WS-Resource’s endpoint
reference contains a SResource identifier in its
ReferenceProperties
•
request message directed
to the WS using that
endpoint reference must
include the S-Resource
identifier.
WS-Resource Relationship
Cardinality
• A WS can execute message exchanges against:
– zero
– more S-Resources defined as instances of the resource property
document.
• A single WS at a particular endpoint is associated with several
individual S-Resources
WS-Resource Relationship
Cardinality (At the type level)
• WSDL 1.1 portType, defining the interface to a WS:
– can be associated with at most one S-Resource property
document.
– S-Resource property document can be associated with many
portTypes.
– Any WS that implements a portType is by definition a WS
associated with a S-Resource
WS-Resource Encapsulation
• Strict encapsulation guarantees that encapsulated data can only
be accessed through well defined operations.
• Data encapsulation facilitates the use of data without the user
having to understand the details of the data implementation
• The implied resource pattern facilitates varying degrees of WS
encapsulation of S-Resources.
WS-Resource Lifecycle
The lifetime of a WS-Resource is defined as the period between
its creation and its destruction.
1.
WS-Resource creation using a WS-Resource factory
2.
Assignment & use of the S-Resource identifier
3.
destruction of a WS-Resource.
WS-Resource Creation
• WS-Resource factory is any WS capable of creating a WSResource
– creating a new S-Resource
– assigning the new S-Resource an identity,
– associating the new S-Resource and its WS.
• The response message of a WS-Resource factory
operation contains
– WS-Resource-qualified endpoint reference containing a SResource identifier that refers to the new S-Resource
WS-Resource Identity
• S-Resource has at least one form of identity that identifies
S-Resource component within the WS-Resource
composition.
• To a WS with a S-Resource is associated:
– the S-Resource identifier carried within a request message is
meaningful.
WS-Resource Identity
• A service requestor that obtains access to a WS-Resourcequalified endpoint reference
– should not examine or attempt to interpret the value of the SResource identifier.
– even comparing the contents of two S-Resource identifiers is
considered invalid.
• From the perspective of the service requestor, the content of
the S-Resource identifier within the endpoint reference is
opaque.
WS-Resource Destruction
• A requestor that wishes to terminate a WS-Resource
uses WS-Resource-qualified endpoint reference to:
– Immediate Destruction: send a destroy request message to
the WS using by the endpoint reference.
– Scheduled Destruction: message exchanges for establishing
and renewing scheduled destruction times on WSResources
WS-Resource Properties
• WS-Resource has an XML resource property document defined
using XML schema.
• Requestors determine a WS-Resource’s type by retrieving the
WSDL portType definition.
• Requestors use WS message exchanges to read, modify, and
query the XML document representing the WS-Resource’s
state.
WS-Resource Properties
• resource property to refer to
– An individual component of a WS-Resource’s state.
– XML document describing the type of a S-Resource within the
WS-Resource is a WS-Resource properties document.
• Each resource property is represented as an XML element
within the WS-Resource properties document
WS-Resource Properties
Document
• WS-Resource properties document acts as a view on, or
projection of, the actual state of the WS-Resource.
– the structure upon which requestor-initiated queries and
updates can be directed.
– Any operation that manipulates a resource property via the
WS-Resource properties document must be reflected in the
actual implementation of the WS-Resource’s state.
WS-Resource Properties
Document
•
the state of “C”
comprises 3 components,
p1, p2, and p3
•
resource properties
document,
“ExampleResourcePropert
ies,”.
WS-Resource Properties
Document
•
WS-Resource properties
document declaration is
associated with the WSDL
portType using a standard
attribute,
resourceProperties
WS-Resource Property
Composition
•
Web services allow to construct a new
interface from several existing interfaces via
a process of composition
•
In WSDL 1.1, this composition must be
achieved by a copy-and-paste of the
operations defined in the constituent
portTypes used in the composition
WS-Resource Property
Composition
• aggregation of WS-Resource properties of the various
constituent portTypes is also possible.
• WS-Resource properties document composition is
obtained by adding additional XML element declarations,
using:
– xs:ref attribute
Accessing WS-Resource
Property Values
• The values of resource properties exposed in the WSResource’s resource properties document, can be
– read, modified, and queried by using standard WS messages.
• The base functionality is to retrieve the value of a single
resource property using a simple WS message exchange
Accessing WS-Resource
Property Values
• Retrieval function allow the retrieval of multiple resource
properties with a single message exchange.
– The WS responds with a message containing the values of the
requested WS-Resource properties
• message exchange to execute an arbitrary Xpath expression
against the resource properties document.
– query expression types may be used to support resource discovery
based on the values of a WS-Resource’s state.