Re: [soa-rm] Definition: Services

[John Harby <jharby@gmail.com>]

Hi George,

    I agree and find some inconsistency in the definition of service
throughout the industry. I've noticed some varying definitions of
"service" from various sources:

"A service in SOA is an exposed piece of functionality with three properties:
	The interface contract to the service is platform-independent. 
	The service can be dynamically located and invoked. 
	The service is self-contained. That is, the service maintains its own
state." BEA Dev2Dev

"A service is a callable routine that is made available over a
network. A service exposes an interface contract, which defines the
behavior of the service and the messages it accepts and returns. The
term service is often used interchangeably with the term provider,
which specifically denotes the entity that provides the service."
    IBM Developerworks

"A service is a unit of work done by a service provider to achieve desired end
results for a service consumer. Both provider and consumer are roles played by
 software agents on behalf of their owners." 
Webservices.xml.com (O'Reilly)

"A service is a function that is well-defined, self-contained, and
does not depend on the context or state of other services."
service-architecture.com


Thanks,
John Harby
http://www.jmhsolutions.com

On 4/13/05, George Ntinolazos <georgios.ntinolazos@stratasoftware.com> wrote:
> Duane, Matt
> 
> What is the 'thing' that you refer to as a 'service'? Is the service a
> 'thing' in the 'real' world, the WSDL file in the hard drive, or the binary
> loaded in the VM or ...? Can you give an example?
> 
> What I am trying to say is that we need to either qualify the term service
> or use alternative terms to distinguish the different forms/views of a
> service thought its lifecycle.
> 
> George
> 
> -----Original Message-----
> From: Duane Nickull [mailto:dnickull@adobe.com]
> Sent: 12 April 2005 17:13
> To: George Ntinolazos
> Cc: 'Don Flinn'; soa-rm@lists.oasis-open.org
> Subject: Re: [soa-rm] Definition: Services
> 
> George:
> 
> Going back to the W3C Technical Note, one of the core principles of
> services is that they are autonomous.  They do not care whether they are
> part of a business process or any other process.  They are self
> sufficient atoms.  The concepts of BPM really belong in a POA reference
> model (which no one has done to my knowledge) or a process oriented view
> of a specific architecture, not in a reference model for service
> oriented architecture.
> 
> Perhaps we should ask the editors to consider this sentence as a
> placeholder:
> => There is no need to make architectural distinctions between a service
> that is consumed as part of a process vs. one that is not.
> 
> I would also assert that a specific architecture can concurrently be
> both SOA and POA.
> 
> Furthermore, another key concept of the W3C WSA is that services are
> independent from underlying implementation technology.  If we start
> looking at the specific function()'s , including one service that
> functionally calls 2 others, we are violating this principle.
> 
> I would like to ask the editors to keep this sentence as a placeholder too:
> => Services are opaque and independent from underlying technology.
> 
> Both of these concepts need to be completely abstract to be included in
> the RM.
> 
> Duane
> 
> George Ntinolazos wrote:
> 
> >I think, in our attempt to define what a service is, we will need to
> >distinguish between the world of business processes and the software world
> >which automates some aspects of those processes. (Here by business, I mean
> >the domain of interest or problem domain)
> >
> >This distinction will allow for qualified terms such as business service,
> >software service, and functional service:
> >
> >A business service represents a step or set of steps within a business
> >process that is atomic and potentially fully automatable. For example, an
> >openAccount business process may contain an atomic step such as
> >identifyCustomer which is a business service.
> >
> >A functional service is a software service which automates all, or part, of
> >a business service. A functional service is an abstraction which defines
> the
> >contractual aspects of a service independently of the implementation
> >technology choices. By definition, is always 'business' focused.
> >
> >A technology service is the realization of all, or part, of a functional
> >service in a given implementation technology. For example, a Java operation
> >invoked using RMI, or a Web Service could both be elements of technology
> >services.
> >
> >
> >A second important distinction is between design-time and runtime. At
> >runtime, objects that offer services may be associated with state. Consider
> >the indetifyCustomer software service. At runtime this software may be
> >associated with more than one set of customers, that is, it might be
> >deployed multiple times pointing to different data. Is this one service or
> >many?
> >
> >Yet another aspect we need to take into account is the service granularity.
> >A service specification can be represented at a number of candidate levels
> >ranging from a typed set of operations (usually referred to as an
> >interface), to the more abstract notion of a set of such interfaces.
> >Further, some existing definitions of service refer to the set of
> interfaces
> >which constitute a particular interaction between parties (for example a
> >CORBA service or a WSDL composition), whereas some focus on the
> >responsibilities of a particular party (or role) within that interaction
> >(Design by Contract approach).
> >
> >George
> >______________________________________
> >George Ntinolazos BSc(Hons), MSc, MBCS
> >
> >Product Director
> >Strata Software Ltd.
> >Office: +44 (0)1483 422515
> >Mobile: +44 (0)7966 652063
> >www.stratasoftware.com
> >Best Practice for Service-Oriented Architectures
> >
> >
> >
> >
> >-----Original Message-----
> >From: Duane Nickull [mailto:dnickull@adobe.com]
> >Sent: 11 April 2005 20:31
> >To: Don Flinn
> >Cc: soa-rm@lists.oasis-open.org
> >Subject: Re: [soa-rm] Definition: Services
> >
> >I do not like this definition since it assumes that all services are
> >used for business processes, which is simply not true.
> >
> >I liked Matt's definition from this morning or some variation of it.  We
> >had one from the SOA Q&A we did and referenced it form the charter.  Not
> >sure if this one still works or if it rubs folks the wrong way.
> >
> >Q: What is a service?
> >
> >A: A service is a contractually defined behavior provided by a component
> >for use by other component(s) based on the contract.
> >
> >Google had too many definitions ranging from Church services to
> >implementation specific definitions.  Didn't find anything there that
> >was abstract.
> >
> >I tried to write another one:
> >
> >Service: an externally visible behavior of a component offered for
> >consumption by other components.  not happy with that.
> >
> >The W3C technical note had a pretty interesting definition, albeit once
> >more implementation specific to WS*:
> >
> >
> >          2.3.2.10 Service
> >
> >
> >            2.3.2.10.1 Definition
> >
> >A service is an abstract resource that represents a capability of
> >performing tasks that represents a coherent functionality from the point
> >of view of provider entities
> ><http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#provider_entity> and
> >requester entities
> ><http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#requester_entity>. To
> >be used, a service must be realized by a concrete provider agent
> ><http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#provider_agent>.
> >
> >
> >            2.3.2.10.2 Relationships to other elements
> >
> >a service is a <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#isa>
> >
> >    resource <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#resource>
> >
> >a service performs
> >
> >    one or more tasks
> >    <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#service_task>
> >
> >a service has <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#hasa>
> >
> >    a service description
> >    <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#service_description>
> >
> >a service has a <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#hasa>
> >
> >    service interface
> >    <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#service_interface>
> >
> >a service has <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#hasa>
> >
> >    service semantics
> >    <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#service_semantics>
> >
> >a service has <http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/#hasa>
> >
> >
> >
> >
> >
> >
> >Duane
> >
> >Services:
> >
> >Don Flinn wrote:
> >
> >
> >
> >>I just ran across a definition of a service in the paper "Composition
> >>Contracts for Service Interaction" Andrade, L. and Fiadeiro, J., which
> >>looks good.
> >>
> >>Slightly modified -
> >>Services are granular software components that can be used as building
> >>blocks for the assembly of business processes.
> >>
> >>Original -
> >>Services can be seen as granular software components that can be used as
> >>building blocks for distributed applications or for the assembly of
> >>business processes.
> >>
> >>Don
> >>
> >>
> >>
> >>
> >>
> >
> >
> >
> 
> --
> ***********
> Senior Standards Strategist - Adobe Systems, Inc. - http://www.adobe.com
> Vice Chair - UN/CEFACT Bureau Plenary - http://www.unece.org/cefact/
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>