01 introduction

Service Oriented
Architecture
Lecture 1: Introduction

95-843: Service Oriented Architecture
Master of Information System 1
Management

Plan for the week

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

Course Web Site
• http://www.andrew.cmu.edu/~mm6

Management

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
Management

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”.
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What is architecture?

Victorian Gothic
or Neo-Gothic
architecture

Management

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.
Management

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 one
95-843: Service Oriented Architecture of Reynolds
Management

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.
Management

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
Management

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 System
Master of Information
Management
12

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
Management

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
Management

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
Master of Information System
Plummer 15
Management of Gartner.

(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.
Management

(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.)
Management

(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

adoptionOrientedstandards.
95-843: Service of Architecture
18
Management

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.
Management

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!
Management

Petri Nets
Consider the following program:
a = 1;
What is the normal process order?
b = 2;
c = 3; Other orderings are possible.
a = a + 1;
c = b + c;
b = a + c;
Management

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).

Management

Petri Nets
Places are typically drawn as circles and transitions as bars.

p1 t1 p2

t3

p3 t2
p4
Management

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 t1 p2

t3

p3 t2
p4
Management

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.

**
t1 p2
p1
t3
* *
t2
p3 p4
Management

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.
Management
26

Fire Transition t1 (ready?)

**
t1 p2
p1
t3
* *
t2
p3 p4
Management

Transition t1 Fired

* *
t1 p2
p1
t3
*
t2
p3 p4
Management

Fire Transition t3 (Ready?)

* *
t1 p2
p1
t3
*
t2
p3 p4
Management

Transition t3 Fired

*
t1 p2
p1
t3

t2
p3 p4
Management

Petri Nets
Consider again the following
program:
a = 1;
b = 2;
c = 3;
a = a + 1;
c = b + c;
b = a + c;
Management

Modeled as a Petri Net
a=1 a=a+1
*
p1 p4
b=2 b=a+c
* p7

p5 c=b+c
p2 p9
c=3
* p8
p6
p3

Management

Fire Transitions (ready?)
a=1 a=a+1
*
p1 p4
b=2 b=a+c
* p7

p5 c=b+c
p2 p9
c=3
* p8
p6
p3

Management

Transitions Fired
a=1 a=a+1
*
p1 p4
b=2 b=a+c
* p7

p5 c=b+c
p2 p9
c=3
*
p8
p6
p3

Management

Fire Transitions (Ready)
a=1 a=a+1
*
p1 p4
b=2 b=a+c
* p7

p5 c=b+c
p2 p9
c=3
*
p8
p6
p3

Management

Transitions Fired
a=1 a=a+1

p1 p4 *
b=2 b=a+c
p7

p5 c=b+c
p2 p9
c=3 *
p8
p6
p3

Management

Fire Last Transition (Ready?)
a=1 a=a+1

p1 p4 *
b=2 b=a+c
p7

p5 c=b+c
p2 p9
c=3 *
p8
p6
p3

Management

Last Transition Fired
a=1 a=a+1

p1 p4
b=2 b=a+c
p7 *

p5 c=b+c
p2 p9
c=3
p8
p6
p3

Management

In This Class

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

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

Management

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. Oriented Architecture
95-843: Service
Management

Liveness
A Petri net is deadlocked if no transition can fire.

A marking M for a Petri net is live if, beginning from M, no
matter what sequence of firings has occurred, it is possible
to fire any given transition by processing through some
additional firing sequence.

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

Management

Deadlock Example
Case:
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.

Management

D available

*
Request D
Request D

D ready D ready

Finished
with D and P Finished
with D and P

Release Process Release
Process
D and P D and P

P ready
P ready

Request P Request P
P available

*
Person 1 Person 2
Management

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 Service Algebra
Petri Nets may be represented with an algebra:

S :: ε  The service that does nothing
X A basic service
S1  S2  S1 followed by S2 Sequence operator
S1 ⊕ S2  S1 xor S2
S1◊ S 2  arbitrary sequence
µS  iteration on S
S1 ||c S2  parallel with communication
(S1S2) --> 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 with
other operations. Oriented Architecture
95-843: Service
Management

The Empty Service

ε P
*

Management

Service S1
S1 *
i1

: :
α
: :

o1

Management

Service S2
S2 *
i2

: β :
γ
: :

o2

Management

Service S3
S3 *
i3

: :
: :

o3

Management

Sequence S1  S2
* i = i1
S1
: :

: :

o1

S2
i2

: :

o=o2
Management

Alternative S1⊕ S2
 i

S1 S2 i2
i1

… …

α β γ

… …

o1 o2

o
Management

Arbitrary Sequence S1 ◊ S2


p1 p2
p3 S2
S1
i1 i2

α β γ

o1 o2

p4 p5
Management

Services µS1
S1
… …

∂
i i1 o


o1

… … ..

Management

Services S1 ||c S2


S2
S1
i1 i2

p1

α β
ϒ

p2

o1 o2

o

Management

Services (S1|S2) ~>S3 

S1 i1 S2 i2

α β γ

o1 o2
p1
This operation is p2
a discriminator.
S1 and S2 may be S3 i3
two services providing Will wait until S1 or
the results of the S2 completes
same complex query.
We take the first o3 Will wait for the later
to complete. one to complete

95-843: Service Oriented Architecture o
Management

Services [S1(p1,q1):Sn(pn,qn)]
i 
send_req_serv
S1 i1 Sn
in

p1 pn

rec_req_1 rec_req_n

send_resp_1 send_resp_n
q1 qn
… …
o1 u on
select_serv

p
… Assume middle branch
q gains info on service
qualities. The two
services provide two
95-843: Service Oriented Architecture entry points.
Master of Information System o 56
Management

An Example of Refinement
 i1
S1
assess_claim

indemnity_customer convoke_customer

o1

Management

An Example of Refinement
i 
S2
 i2
assess_simple_claim assess_complex_claims
assess_simple_claim assess_complex_claim

indemnify_customer convoke_customer

o2

o

Ref(S1,assess_claim,S2)
Management

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

OCS : Online Computing Store
SM : Sony Monitors
IP : Intel Processors

The Online Computing Store needs Sony monitors and
Intel processors.

Management

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

 OCS || c2 IP
OCS
SM
rec_ord_pc IP

rec_ord_mon rec_ord_pr
send_ord_pr
send_ord_mon
send_del_mon

rec_del_pr send_del_pr

rec_del_mon

assemble_PC

o
Management

A Quiz
Describe this web service in words.

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

Management

Properties of The Service Algebra
Each operation returns a web service.

S1 (S2  S3) = (S1 S2)  S3 (1)

εS=S (2)
Sε=S (3)
S1 ⊕ S2 = S 2 ⊕ 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)

Management

Desired Properties of the Service Algebra

µε=ε (9)

S1 ||c S2 = S2 ||c S1 (10)

S1 ||∅(S2 ||∅ S3) = (S1 ||∅ S2) ||∅ S3 (11)

S ||∅ ε = S (12)

(S1|S2) ~>S3 = (S2|S1) ~> S3 (13)

(S1 | ε ) ~> S2 = S1 ||∅ S2 (14)

(S1|S2) ~> ε = S1 ||∅ S2 (15)

Management

Desired Properties of the Service Algebra

n (16)
∀{i1,…,in} ={1,…,n} ∏ Si= ∏ Si
Select the best of n services
w/o concern for initial state names. i ∈{i ,…,i }
i=1
1 n

n n
(17)
If Sj = ε then ∏ Si = ∏ Si Don’t select the
empty service.
i=1 i=1,i≠j
If a is not an operation
Ref(S1,a,S2) = S1 if a ∉ L1(T1) then no refinement.
(18)

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

S ◊ S = S  S (from (8) and (6)) (20)

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

Example Proof
Prove: S1 ◊ S2 = S2 ◊ S1

S1 ◊ S2 = (S1  S2) ⊕ (S2  S1)

(S1  S2) ⊕ (S2  S1) = (S2  S1) ⊕ (S1  S2) = S2 ◊ S1

Management

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