01 introduction

95-843: Service Oriented Architecture1Master of Information System

Management

Service Oriented Architecture

Lecture 1: Introduction


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Plan for the week

• Course Introduction• Some principles and definitions• Some Theory• Technology Foundations• Homework 1 • Getting logged on to Oracle’s SOA Suite


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Course Web Site

• http://www.andrew.cmu.edu/~mm6


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Course Software

• We will be using Oracle SOA Suite 11g R1 for projects and demonstrations.• It will be assumed the the student is able to

program in Java and use an IDE.


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Structure of the Course

• Lectures/class participation• Homework (pencil and paper and

programming)• Midterm exam• Readings from IBM’s High level

reference architecture will be assigned. • Reading from the required course text

and the web will be assigned.• Presentations• Final examination


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Readings

• For this week, read the Introduction to Petri Nets and the paper “A Petri Net-based Model for Web Service Composition”.

• Read Chapter One of “Oracle SOA Suite 11g R1”.

• Read the Introduction and Chapter 1 of “Understanding SOA with Web Services”.

95-843: Service Oriented Architecture

What is architecture?

7Master of Information System Management

Victorian Gothic or Neo-Gothicarchitecture


Architecture From Reynolds Text

• Architecture implies a consistent and coherent design approach. Essential principles include:

• Consistency: The same challenges should be addressed in a uniform way.• Reliability: The structures created must be fit to purpose

and meet the demands for which they are designed.• Extensibility: A design must provide a framework that

can be expanded in ways both foreseen and unforeseen.

• Scalability: The implementation must be capable of being scaled to accommodate increasing load by adding hardware to the solution.



Why is SOA Different?

(1) Terminology: Both IT people and

business people know what a service is.(2) Interoperability: The interfaces and the wire protocols are based on standards.(3) Extension and Evolution not rip and replace.(4) Reuse of both functionality and machine resources.


Chapter oneof Reynolds


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SOA Defined

• “SOA is the architectural style that supports loosely coupled services to enable business flexibility in an interoperable, technology agnostic manner. SOA consists of a composite set of business-aligned services that support a flexible and dynamically re-configurable end-to-end business process realization using interface-based service descriptions.” From a paper by Borges, Holley and Arsanjani.


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Web Services Preferred(1)

• Web Services are XML-based technologies for messaging, service descriptions, discovery, and external features providing:

- Pervasive open standards for distributed computing interface descriptions and document exchange via messages

From Newcomer


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Web Services Preferred(2)

- Independence from the underlying execution environment and application platforms. - Extensibility for enterprise qualities of service such as security, reliability, and transactions. - Support for composite applications such as business process flows, multi-channel access, and rapid integration


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XML Preferred (1)

• The Extensible Markup Language is a common, independent data format across the enterprise and beyond that provides:

- Standard data types and structures, independent of any programming language, development environment or software system.

From Newcomer


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XML Preferred (2)

- Pervasive technology for defining business documents and exchanging business information, including standard vocabularies for many industries.

- Ubiquitous software for handling operations on XML, including parsers, queries, and transformations.

From Newcomer


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Build an SOA in 8 Steps

(1) Business needs come first (not services) What problem are we trying to solve?(2) What aspects can be implemented as services? Old services? New services? Legacy wrappers?(3) Track services with registries and

repositories.Modified from a talk by Daryl Plummerof Gartner.


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(4) Govern the services. We need to encourage desired behavior at many levels, across enterprises, and at different stages. We need to monitor behavior, enforce policies & assess user satisfaction.


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(5) Secure the services. Using established standards, we need privacy, identification, authentication, and authorization. This may need to be federated security (over more than one organization.)


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(6) Manage the services. Are messages arriving on time? Is everything operating properly?(7) Virtualization through mediation. Are we free to move and change the services? Do we need an ESB that acts

as a central hub for message routing and transformations?

(8) Design for interoperability through the adoption of standards.


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Objectives of This Course(1) Study Foundations of SOA Mathematical models (Petri nets) Important standards Orchestration and Choreography The Enterprise Service Bus Reference Architectures Enterprise Integration Patterns(2) Get hands on experience with Oracle’s SOA Suite of tools.


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A Mathematical Foundation

• Petri Nets• Petri Nets as applied to Web

Services• Why not flow charts?• Why not UML sequence diagrams?• We want to work at a higher level

and exploit parallel execution.• Plus, Petri nets are cool!


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Petri Nets

Consider the following program: a = 1; b = 2; c = 3; a = a + 1; c = b + c; b = a + c;

What is the normal process order?

Other orderings are possible.


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Petri Nets

A Petri net is a directed graph G = (V,E), where V = P U T and P T = . Any edge e in E is incident on one member of P and one member of T. The set P is called the set of places (conditions) and the set T is the set of transitions (events).


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Petri Nets

p1

p3

t1

t2

p2

p4

t3

Places are typically drawn as circles and transitions as bars.


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Petri Net G = (V,E)P = {p1,p2,p3,p4}T = {t1,t2,t3}E = {(p1,t1),(t1,p2),(p2,t3),(p3,t1),(p3,t2),(t2,p4),(p4,t3)}

p1

p3

t1

t2

p2

p4

t3


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A Marked Petri Net A marking of a Petri net assigns each place a

nonnegative integer n. We say each place p is marked with n tokens. Tokens are represented as black dots.

**

* *

p1

p3

t1

t2

p2

p4

t3


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Firing Transitions

In a Petri net, if an edge is directed from place p to transition t, we say p is an input place for transition t. An output place is defined similarly. If every input place for a transition t has at least one token, we say that t is enabled. A firing of an enabled transition removes one token from each input place and adds one token to each output place. A transition can fire only if it’s enabled. Firing a transition is an atomic operation.


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Fire Transition t1 (ready?)

* *

p1

p3

t1

t2

p2

p4

t3

**


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Transition t1 Fired

*

*

p1

p3

t1

t2

p2

p4

t3

*


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Fire Transition t3 (Ready?)

*

*

p1

p3

t1

t2

p2

p4

t3

*


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Transition t3 Fired

p1

p3

t1

t2

p2

p4

t3

*


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Petri Nets

Consider again the following program:

a = 1; b = 2; c = 3; a = a + 1; c = b + c; b = a + c;


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Modeled as a Petri Net

*

*

*

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c


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Fire Transitions (ready?)

*

*

*

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c


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Transitions Fired

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c

*

*

*


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Fire Transitions (Ready)

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c

*

*

*


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Transitions Fired

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c*

*


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Fire Last Transition (Ready?)

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c*

*


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Last Transition Fired

p1

p2

p3

p4

p5

p6

p7

p8

p9

a=1

b=2

c=3

a=a+1

c=b+c

b=a+c

*


In This Class


All of our Petri Nets will begin with a single input place andend with a single output place.

We will always start the Petri Net off with a single token in theinput place.


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Two Quizzes (Take out pencil and paper)

(1) The Petri Net we drew begins with three markings.Redraw the Petri net so that it begins with a single marking.

(2) Build a Petri net to wash a lion based on the following steps.

1. Get lion. 2. Get soap. (real soap not SOAP) 3. Get tub. 4. Put water in tub. 5. Put lion in tub. 6. Wash lion with soap. 7. Rinse lion. 8. Remove lion from tub. 9. Dry lion.


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Liveness

A Petri net is deadlocked if no transition can fire.

A marking M for a Petri net is live if, beginning from M, nomatter what sequence of firings has occurred, it is possibleto fire any given transition by processing through someadditional firing sequence.

If a marking M is live for a Petri net P, then no matter whatsequence of transitions is fired, P will never deadlock. Indeed,we can fire any transition by proceeding through some additional firing sequence.


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Deadlock ExampleCase: Person 1 requests disk drive D. D is ready. Person 1 requests printer P. P is ready. Person 1 uses and releases P and D. P and D are available.

Case: Person 1 requests disk drive D. D is ready. Person 2 requests printer P. P is ready. Person 1 is waiting for person 2 to release P. Person 2 is waiting for person 1 to release D. No transitions can fire and we have deadlock.


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D available

Request D

D ready

Finished with D and P

ReleaseD and P

Request D

D ready

Finished with D and P

Process Process

P ready

Request P Request PP available

ReleaseD and P

*

P ready

Person 1 Person 2

*


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Deadlock


Four Requirements for deadlock:

(1) Resources need mutual exclusion. They are not thread safe. (2) Resources may be reserved while a process is waiting for more. (3) Preemption is not allowed. You can't force a process to give up a resource. (4) Circular wait is possible. X wants what Y has and Y wants what Z has but Z wants what X has.

Solutions (short course):

Prevention (disallow one of the four) Avoidance (study what is required by all before beginning) Detection and recovery (reboot if nothing is getting done)


Management

Petri Nets may be represented with an algebra:

S :: The service that does nothing X A basic service S1 S2 S1 followed by S2 Sequence operator S1 S2 S1 xor S2

S1◊ S2 arbitrary sequence µS iteration on S

S1 c S2 parallel with communication

(S1S2) --> S3 As soon as S1 or S2 do S3

[S1(p1,q1):(SN(pn,qn)]| dynamically select one of many to execute Ref(S1,a,S2) Do S1 with any ‘a’ operations replaced by S2

Each operation returns a service that may or may not be involved withother operations.

Petri Nets Service Algebra


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*

P

The Empty Service


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*

: :

:

Service S1

S1i1

o1

:


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*

: :

:

Service S2

S2i2

o2

:


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*

: :

:

Service S3

S3i3

o3

:


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*

: :

: :

Sequence S1 S2

: :

i = i1

i2

o=o2

S1

S2

o1


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Alternative S1 S2

i

i1i2

o

o1 o2

… …

… …

S1S2


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Arbitrary Sequence S1 ◊ S2

S1S2

p1

p3

p2

i2i1

p5p4

o2o1


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S1

o

o1

i1i

Services µS1

… …

… … ..


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S1

S2

i2

o2

o

o1

i1

Services S1 ||c S2

p1

p2


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o

o3

Services (S1|S2) ~>S3

p1

p2

o2

S2

S1 i1 i2

o1

S3i3

Will wait until S1 or S2 completes

Will wait for the later one to complete

This operation isa discriminator.S1 and S2 may betwo services providingthe results of the same complex query. We take the first to complete.


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…

……

o1on

q1qn

send_resp_1 send_resp_n

rec_req_nrec_req_1

p1pn

i1

in

select_servu

send_req_serv Sn

q

S1

p

o

Assume middle branch gains info on service qualities. The two services provide two entry points.

Services [S1(p1,q1):Sn(pn,qn)]i


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An Example of Refinement

assess_claim

indemnity_customer convoke_customer

S1

o1

i1


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An Example of Refinement

i2

o2

assess_simple_claim assess_complex_claim

o

i

Ref(S1,assess_claim,S2)

indemnify_customer

assess_simple_claim

convoke_customer

assess_complex_claims

S2


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Example Service (SM ||c1( OCS|| c2 IP))

OCS : Online Computing StoreSM : Sony MonitorsIP : Intel Processors

The Online Computing Store needs Sony monitors andIntel processors.


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Example Service SM ||c1( OCS|| c2 IP)

IP

rec_ord_pr

send_del_pr

OCS

send_ord_pr

rec_del_pr

assemble_PC

rec_del_mon

send_ord_mon

rec_ord_pc

SM

rec_ord_mon

send_del_mon

o

OCS || c2 IP


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A QuizDescribe this web service in words.

Ref(S1, assess_claim, [A1:An])


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Properties of The Service Algebra

S1 (S2 S3) = (S1 S2) S3 (1)

S = S (2)

S = S (3)

S1 S2 = S2 S1 (4)

S1 (S2 S3) = (S1 S2) S3 (5)

S S = S (6)

(S1 S2) S3 = (S1 S3)(S2 S3) (7)

S1 S2 = (S1 S2) (S2 S1) (8)

Each operation returns a web service.


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Desired Properties of the Service Algebra

= (9)

S1 c S2 = S2 c S1 (10)

S1 (S2 S3) = (S1 S2) S3 (11)

S = S (12)

(S1S2) ~>S3 = (S2S1) ~> S3 (13)

(S1 ) ~> S2 = S1 S2 (14)

(S1S2) ~> = S1 S2 (15)


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Desired Properties of the Service Algebra

{i1,…,in} ={1,…,n} Si= S

i

(16)

If Sj = then Si = Si

(17)

Ref(S1,a,S2) = S1 if a L1(T1) (18)

S1 S2 = S2 S1 (from (8) and (4)) (19)

S S = S S (from (8) and (6)) (20)

S = S (from (8), (2), (3), and (6)) (21)

i {i1,…,in}i=1

n

n

i=1 i=1,ij

n

Select the best of n servicesw/o concern for initial state names.

Don’t select the empty service.

If a is not an operation then no refinement.


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Example ProofProve: S1 S2 = S2 S1

S1 S2 = (S1 S2) (S2 S1)

(S1 S2) (S2 S1) = (S2 S1) (S1 S2) = S2 S1

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01 introduction