Expert answer:Service Oriented Architecture Concepts
Expert answer:Unit 2 Discussion How can an organizations balance the competing needs of the significant up-front analysis required for SOA with the time constraints on the application development process? Support your opinion Requirements: – Learner successfully addressed the concept(s) of the Discussion topic – 5 pts max. – Learner successfully incorporates a minimum of two scholarly sources in the initial post to support their position – 5 pts max. – Learner met the criteria for academic writing (i.e. no spelling or grammar errors, properly formatted paragraphs, APA formatting used for references, etc.) – 5 pts max. – Learner met the 250-word count minimumreference of the reading material is provided is
Erl, T. (2008). SOA principles of service design (1st ed.). Boston, MA: Prentice Hall.
https___vcampbethel.blob.core.windows.net_public_courses_it_4531_unit_2_read.pdf
Unformatted Attachment Preview
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 67
Chapter 4
W
I
L
S
O
N
,
J
A
M
I
E
Introduction to Service-Orientation
5
Problems Solved by Service-Orientation
0
Challenges Introduced by Service-Orientation
5
Additional Considerations 1
B
Effects of Service-OrientationUon the Enterprise
Origins and Influences of Service-Orientation
Service-Orientation
4.1
4.2
4.3
4.4
4.5
4.6
4.7 Case Study Background
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 68
H
aving covered some of the basic elements of service-oriented computing, we now
narrow our focus on service-orientation. The next set of sections establish the
paradigm of service-orientation and explain how it is changing the face of distributed
W
computing.
I
L
4.1 Introduction to Service-Orientation
S
In the every day world around us, services are and have been commonplace for as long
O
as civilized history has existed. Any person carrying out a distinct task in support of othN of individuals collectively performing
ers is providing a service (Figure 4.1). Any group
a task is also demonstrating the delivery of a ,service.
Figure 4.1
Three individuals, each capable of providing a distinct
service.
J
A
M
I
E
Similarly, an organization that carries out tasks
5 associated with its purpose or business
is also providing a service. As long as the task 0
or function being provided is well-defined
and can be relatively isolated from other associated tasks, it can be distinctly classified
5
as a service (Figure 4.2).
1
Certain baseline requirements exist to enable a group of individual service providers to
B service. Figure 4.2, for example, discollaborate in order to collectively provide a larger
plays a group of employees that each provideUa service for ABC Delivery. Even though
each individual contributes a distinct service, for the company to function effectively, its
staff also needs to have fundamental, common characteristics, such as availability, reliability, and the ability to communicate using the same language. With all of this in place,
these individuals can be composed into a productive working team. Establishing these
types of baseline requirements is a key goal of service-orientation.
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 69
69
4.1 Introduction to Service-Orientation
Figure 4.2
A company that employs these three people can compose
their capabilities to carry out its business.
W
I
L
S
O
N
,
Services in Business Automation
J
In the world of SOA and service-orientation, the term “service” is not generic. It has speA
cific connotations that relate to a unique combination
of design characteristics. When
M
solution logic is consistently built as services
and when services are consistently
designed with these common characteristics,
I service-orientation is successfully realized
throughout an environment.
E
For example, one of the primary service design characteristics explored as part of this
study of service-orientation is reusability. A strong emphasis on producing solution
5
logic in the format of services that are positioned as highly generic and reusable enter0
prise resources gradually transitions an organization
to a state where more and more of
its solution logic becomes less dependent 5
on and more agnostic to any one purpose or
business process. Repeatedly fostering this
1 characteristic within services eventually
results in wide-spread reuse potential.
B
Consistently realizing specific design characteristics
requires a set of guiding principles.
U
This is what the service-orientation design paradigm is all about.
Services Are Collections of Capabilities
When discussing services, it is important to remember that a single service can provide
a collection of capabilities. They are grouped together because they relate to a functional
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 70
70
Chapter 4: Service-Orientation
context established by the service. The functional context of the service illustrated in
Figure 4.3, for example, is that of “shipment.” Therefore, this particular service provides
a set of capabilities associated with the processing of shipments.
Figure 4.3
Much like a human, an automated service
can provide multiple capabilities.
W
I
L
S
A service can essentially act as a container of related capabilities. It is comprised of a
body of logic designed to carry out theseO
capabilities and a service contract that
expresses which of its capabilities are made available
for public invocation.
N
References to service capabilities in this book, are specifically focused on those that are
defined in the service contract. For a discussion of how service capabilities are distinguished from Web service operations and component methods, see the Principles and
J
Service Implementation Mediums section in Chapter 5.
A
M
Service-Orientation as a Design Paradigm
I
As established in Chapter 3, a design paradigm is an approach to designing solution
E design approaches revolve around a
logic. When building distributed solution logic,
software engineering theory known as the separation of concerns. In a nutshell, this theory states that a larger problem is more effectively
5 solved when decomposed into a set
of smaller problems or concerns. This gives us the option of partitioning solution logic
0
into capabilities, each designed to solve an individual concern. Related capabilities can
5
be grouped into units of solution logic.
1
The fundamental benefit to solving problems this way is that a number of the solution
B concerns while still remaining agnostic
logic units can be designed to solve immediate
to the greater problem. This provides the constant
opportunity for us to reutilize the
U
capabilities within those units to solve other problems as well.
Different design paradigms exist for distributed solution logic. What distinguishes service-orientation is the manner in which it carries out the separation of concerns and how
it shapes the individual units of solution logic. Applying service-orientation to a meaningful extent results in solution logic that can be safely classified as “service-oriented”
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 71
4.1 Introduction to Service-Orientation
71
and units that qualify as “services.” To understand exactly what that means requires an
appreciation of the strategic goals covered in Chapter 3 combined with knowledge of the
associated design principles documented in Part II.
For now, let’s briefly introduce each of these principles:
Standardized Service Contract
Services express their purpose and capabilities
W via a service contract. The Standardized
Service Contract design principle is perhaps the most fundamental part of serviceI
orientation in that it essentially requires that specific considerations be taken into
account when designing a service’s publicLtechnical interface and assessing the nature
and quantity of content that will be published
S as part of a service’s official contract.
O aspects of contract design, including the
A great deal of emphasis is placed on specific
manner in which services express functionality,
how data types and data models
N
are defined, and how policies are asserted and attached. There is a constant focus on
,
ensuring that service contracts are both optimized, appropriately granular, and standardized to ensure that the endpoints established by services are consistent, reliable,
J
and governable.
A principle in detail.
Chapter 6 is dedicated to exploring this design
M
Service Loose Coupling
I
Coupling refers to a connection or relationship
E between two things. A measure of coupling is comparable to a level of dependency. This principle advocates the creation of a
specific type of relationship within and outside of service boundaries, with a constant
5
emphasis on reducing (“loosening”) dependencies
between the service contract, its
0
implementation, and its service consumers.
5
The principle of Service Loose Coupling promotes
the independent design and evolution of a service’s logic and implementation
1 while still guaranteeing baseline interoperability with consumers that have come toBrely on the service’s capabilities. There are
numerous types of coupling involved in the design of a service, each of which can
U
impact the content and granularity of its contract. Achieving the appropriate level of
coupling requires that practical considerations be balanced against various service
design preferences.
Chapter 7 provides an in-depth exploration of this principle and introduces related patterns and concepts.
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 72
72
Chapter 4: Service-Orientation
Service Abstraction
Abstraction ties into many aspects of service-orientation. On a fundamental level, this
principle emphasizes the need to hide as much of the underlying details of a service as
possible. Doing so directly enables and preserves the previously described loosely coupled relationship. Service Abstraction also plays a significant role in the positioning and
design of service compositions.
Various forms of meta data come into the picture
W when assessing appropriate abstraction levels. The extent of abstraction applied can affect service contract granularity and
I
can further influence the ultimate cost and effort of governing the service.
L
Chapter 8 covers several aspects of applying abstraction to different types of service
S
meta data, along with processes and approaches associated with information hiding.
O
Service Reusability
N
Reuse is strongly advocated within service-orientation;
so much so, that it becomes a
,
core part of typical service analysis and design processes, and also forms the basis for
key service models. The advent of mature, non-proprietary service technology has proJ
vided the opportunity to maximize the reuse potential of multi-purpose logic on an
A
unprecedented level.
M the positioning of services as enterprise
The principle of Service Reusability emphasizes
I
resources with agnostic functional contexts. Numerous
design considerations are raised
to ensure that individual service capabilities E
are appropriately defined in relation to an
agnostic service context, and to guarantee that they can facilitate the necessary reuse
requirements.
5
Variations and levels of reuse and associated agnostic service models are covered in
0
Chapter 9, along with a study of how commercial product design approaches have
5
influenced this principle.
1
B
For services to carry out their capabilities consistently
and reliably, their underlying
U
Service Autonomy
solution logic needs to have a significant degree of control over its environment and
resources. The principle of Service Autonomy supports the extent to which other design
principles can be effectively realized in real world production environments by fostering
design characteristics that increase a service’s reliability and behavioral predictability.
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 73
4.1 Introduction to Service-Orientation
73
This principle raises various issues that pertain to the design of service logic as well as
the service’s actual implementation environment. Isolation levels and service normalization considerations are taken into account to achieve a suitable measure of autonomy,
especially for reusable services that are frequently shared.
Chapter 10 documents the design issues and challenges related to attaining higher
levels of service autonomy, and further classifies different forms of autonomy and
highlights associated risks.
W
I
Service Statelessness
L
The management of excessive state information
can compromise the availability of a
service and undermine its scalability potential.
Services
are therefore ideally designed to
S
remain stateful only when required. Applying
O the principle of Service Statelessness
requires that measures of realistically attainable statelessness be assessed, based on the
N
adequacy of the surrounding technology architecture to provide state management del,
egation and deferral options.
Chapter 11 explores the options and impacts of incorporating stateless design characJ
teristics into service architectures.
A
M
For services to be positioned as IT assets with repeatable ROI they need to be easily idenI
tified and understood when opportunities for reuse present themselves. The service
E
design therefore needs to take the “communications
quality” of the service and its indiService Discoverability
vidual capabilities into account, regardless of whether a discovery mechanism (such as
a service registry) is an immediate part of the
5 environment.
The application of this principle, as well as0
an explanation of how discoverability relates
to interpretability and the overall service discovery
process, are covered in Chapter 12.
5
1
B
As the sophistication of service-oriented solutions continues to grow, so does the comU
plexity of underlying service composition configurations.
The ability to effectively comService Composability
pose services is a critical requirement for achieving some of the most fundamental goals
of service-oriented computing.
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 74
74
Chapter 4: Service-Orientation
Complex service compositions place demands on service design that need to be anticipated to avoid massive retro-fitting efforts. Services are expected to be capable of participating as effective composition members, regardless of whether they need to be
immediately enlisted in a composition. The principle of Service Composability
addresses this requirement by ensuring that a variety of considerations are taken into
account.
How the application of this design principle helps prepare services for the world of comW
plex compositions is described in Chapter 13.
I
Service-Orientation and Interoperability L
S
One item that may appear to be absent from the preceding list is a principle along the
lines of “Services are Interoperable.” The reasonOthis does not exist as a separate principle
is because interoperability is fundamental to N
every one of the principles just described.
Therefore, in relation to service-oriented computing, stating that services must be inter,
operable is just about as basic as stating that services must exist. Each of the eight principles supports or contributes to interoperability in some manner.
J
A
Service contracts are standardized to guarantee a baseline measure of interoperM
ability associated with the harmonization of data models.
I
Reducing the degree of service coupling fosters interoperability by making indiE
vidual services less dependent on others and therefore more open for invocation
Here are just a few examples:
•
•
by different service consumers.
5 all interoperation to the service con• Abstracting details about the service limits
0 of interoperability by allowing underlytract, increasing the long-term consistency
ing service logic to evolve more independently.
5
1
• Designing services for reuse implies a high-level
of required interoperability
between the service and numerous potential
service
consumers.
B
• By raising a service’s individual autonomy,
U its behavior becomes more consistently predictable, increasing its reuse potential and thereby its attainable level of
interoperability.
• Through an emphasis on stateless design, the availability and scalability of services increase, allowing them to interoperate more frequently and reliably.
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 75
75
4.2 Problems Solved by Service-Orientation
• Service Discoverability simply allows services to be more easily located by those
who want to potentially interoperate with them.
• Finally, for services to be effectively composable they must be interoperable. The
success of fulfilling composability requirements is often tied directly to the extent
to which services are standardized and cross-service data exchange is optimized.
A fundamental goal of applying service-orientation is for interoperability to become a
natural by-product, ideally to the extent that
Wa level of intrinsic interoperability is established as a common and expected service design
characteristic. Depending on the archiI
tectural strategy being employed, this extent may or may not be limited to a specific
L
service inventory.
S
Of course, as with any other design characteristic, there are levels of interoperability a
service can attain. The ultimate measure isO
generally determined by the extent to which
N
service-orientation principles have been consistently and successfully realized (plus, of
course, environmental factors such as the ,compatibility of wire protocols, the maturity
level of the underlying technology platform, and adherence to technology standards).
J
A
Increased intrinsic interoperability is one of the key strategic goals associated with service-oriented computingM
(as originally established in Chapter
3). For more detailed information about how service-orientation principles
I
directly support this and other strategic goals, see Chapter 16.
E
NOTE
SUMMARY OF KEY POINTS
5 of eight distinct design principles,
• The service-orientation paradigm consists
each of which fosters fundamental design
0 characteristics, such as interoperability. These principles are explored individually in subsequent chapters.
5
• Interoperability is a natural by-product of applying service-orientation design
1
principles.
B
U
4.2 Problems Solved by Service-Orientation
To best appreciate why service-orientation has emerged and how it is intended to
improve the design of automation systems, we need to compare before and after perspectives. By studying some of the common issues that have historically plagued IT, we
can begin to understand the solutions proposed by this design paradigm.
SOA Principles of Service Design, First Edition, by Thomas Erl. Published by Prentice Hall. Copyright © 2008 by Pearson Education, Inc.
05_0132344823_04.qxd
6/13/07
4:44 PM
Page 76
76
Chapter 4: Service-Orientation
NOTE
This book fully acknowledges that past design paradigms have advocated similar principles and strategic goals as service-orientation. Several
of these design approaches, in fact, directly inspired or influenced service-orientation (as explained further in the Origins and Influences of Service-Orientation section of this chapter). The following section is focused
specifically on a comparison with the silo-based design approach
because it has persisted as the most common
W means by which applications are delivered.
I
L
Life Before Service-Orientation
S
In the world of business it makes a great deal of sense to deliver solutions capable of
O the course of IT’s history, the majority
automating the execution of business tasks. Over
of such solutions have been created with a common
N approach of identifying the business
tasks to be automated, defini …
Purchase answer to see full
attachment
How it works
- Paste your instructions in the instructions box. You can also attach an instructions file
- Select the writer category, deadline, education level and review the instructions
- Make a payment for the order to be assignment to a writer
- Download the paper after the writer uploads it
Will the writer plagiarize my essay?
You will get a plagiarism-free paper and you can get an originality report upon request.
Is this service safe?
All the personal information is confidential and we have 100% safe payment methods. We also guarantee good grades