Introduction and Overview
Peter Bunus
Department of Computer and Information Science
Linköping University, Sweden peter.bunus@liu.se

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Component-Based Development
In this course you will learn to develop building blocks
“ components ” that you or someone else can assemble or reassemble into different applications
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Look at the Amazon main webpage and quickly identify some elements that you consider to be software components.
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Clemens Szyperski: Component Software –
Beyond Object-Oriented Programming .
Second Edition, Addison-Wesley – Second Edition
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Managing system complexity: Divide-and-conquer (Alexander the
Great)
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Well known in other disciplines
•   Mechanical engineering (e.g., German DIN 2221; IEEE standards)
•   Electrical engineering
•   Architecture
•   Computer architecture
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Outsourcing to component produces
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Reuse of partial solutions
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Easy configurability of the systems
•   Variants, versions, product families
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Every ripe industry is based on components, since these allow to manage large systems
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Components should be produces in masses and composed to systems afterwards
Mass Produced Software Components by M.D McIlroy
"Software Engineering, Report on a conference sponsored by the NATO
Science Committee, Garmisch, Germany, 7th to 11th October 1968",
Scientific Affairs Division, NATO,Brussels, 1969, 138-155.
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In the phrase “ mass production techniques ”, my emphasis is on “ techniques ” and not on mass production plain. Of course, mass production, in the sense of limitless replication of a prototype, is trivial for software
M.D McIlroy
But certain ideas from industrial technique I claim are relevant.
- The idea of subassemblies carries over directly and is well exploited.
- The idea of interchangeable parts corresponds roughly to our term “modularity”, and is fitfully respected.
- The idea of machine tools has an analogue in assembly programs and compilers
Yet this fragile analogy is belied when we seek for analogues of other tangible symbols of mass production.
- There do not exist manufacturers of standard parts, much less catalogues of standard parts.
- One may not order parts to individual specifications of size, ruggedness, speed, capacity, precision or character set . 8

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“ A software component is a software element that conforms to a component model and can be independently deployed and composed without modification according to a composition standard.
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A component model defines specific interaction and composition standards.
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Composition is the combination of two or more software components yielding a new component behavior at a different level of abstraction ...
[which is] determined by the components being combined and the way how they are combined.
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Heineman / Councill [Ch.1]:
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Object Properties
•   An object is a unit of instantiation.
•   It has a unique identity.
•   It may have state, and this can be (externally) observed
•   It encapsulates its state and behavior.
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Components
•   Components are rather prototypes / blueprints / plansfrom which (stateful) objects can be instantiated
–   e.g., a function definition, type definition, class or set of classes
•   No (externally observable) state
•   Unit of independent deployment
•   Unit of third-party composition
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We call a technology in which component-based systems can be produced a component system or component platform .
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A component system has
Component Model for description of components
Composition Technique for compositions of components
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A Software Composition System has
Component Model for description of components
Composition
Language for programming-in-thelarge and architecture
Composition Technique for compositions of components
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Component Model
•   How do components look like?
•   Secrets? (Location, lifetime, language, platform, … )?
•   Binding points, binding time?
•   Interfaces, contracts, substitutability?
•   Parameterizability? Adaptability? Extensibility?
•   Standardization of execution environment, services?
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Composition Technique
•   How are components glued together, composed, merged, applied?
•   Composition time (Compile- / Link- / Deployment- / Connection- / Run-time ...)
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Composition Language
•   How are compositions of large systems described and managed?
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Procedural systems
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Modular systems
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Object-oriented technology
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Component-based programming with COTS (Components-off-the-shelf) systems
•   CORBA, EJB, DCOM, COM+, .NET
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Software architecture description languages
BlackBox Composition
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Components
Connectors
Composition recipe
Component-based applications

SOA: SW architecture where all components are designed to be services !
1.
All teams will henceforth expose their data and functionality through service interfaces "
2.
Teams must communicate with each other through these interfaces "
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There will be no other form of interprocess communication allowed: no direct linking, no direct reads of another team's data store, no shared-memory model, no back-doors whatsoever. The only communication allowed is via service interface calls over the network. "
Taken from: CS 169 Software Engineering: Armando Fox, David Patterson, and Koushik Sen !
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4.
It doesn't matter what [API protocol] technology you use. "
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Service interfaces, without exception, must be designed from the ground up to be externalizable. That is to say, the team must plan and design to be able to expose the interface to developers in the outside world. No exceptions. "
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Anyone who doesn't do this will be fired. "
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Thank you; have a nice day!
“ "
Taken from: CS 169 Software Engineering: Armando Fox, David Patterson, and Koushik Sen !
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Internal subsystems can share data directly !
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Review access user profile !
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All subsystems inside single API
( “ Bookstore ” ) !
reviews users
Review
Subsystem
User Profile
Service orders
Buying
Subsystem
Bookstore Service
(Figure 1.2, Engineering Long
Lasting Software by Armando Fox and David Patterson, Alpha edition,
2012.)
Taken from: CS 169 Software Engineering: Armando Fox, David Patterson, and Koushik Sen !
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•   Subsystems independent, as if in separate datacenters !
–   Review Service access
User Service API !
•   Can recombine to make new service ( “ Favorite Books ” ) !
Taken from: CS 169 Software Engineering: Armando Fox, David Patterson, and Koushik Sen !
users
Social
Network
Service
credit card processing user reviews editor reviews
Review
Service users
User Profile
Service orders
Buying
Service
Bookstore Service
Favorite Books
Service
(Figure 1.3, Engineering Long
Lasting Software by Armando Fox and David Patterson, Alpha edition,
2012.)
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Fortran, Algol, Pascal, C, ...
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The procedure is the component
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The activation record the instantiation
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Component model is supported by almost all processors directly
•   JumpSubroutine instruction
•   Return instruction
Caller
(code)
Callee
(code)
Linker
Caller-
AR call
Callee-
AR
Caller AR addr.
Return address
Caller-
AR ret
Caller-
AR
Run time
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Component Model
Content: binary code with symbols
Binding points: linker symbols procedures (with parameters) and global variables
Composition Technique
Connection by linking object files
Program transformation on object files
Composition time: link-time, static
Composition Language
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What this UNIX command does?
$ cat apple.txt
$ cat apple.txti
Ipad iphone macbook
$ cat apple.txt | wc at this first shell prompt, we show the contents of the file apple.txt on the screen
$ cat apple.txt | wc
4 6 7 the standard output of the command to the left of the pipe gets sent as standard input of the command to the right of the pipe.
We use the cat command to display the contents of the apple.txt file, but I sent the display not to the screen, but through a pipe to the wc (word count) command. The wc command then does its job and counts the lines, words, and characters of what it got as input
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UNIX shells style still offers the most used component paradigm:
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Communication with byte streams via standard I/O ports
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Parsing and linearizing the objects
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Extremely flexible, simple stderr stdin
Filter stdout stdin
Filter pipe
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Component Model
Content: unknown (due to parsing), externally bytes
Binding points: stdin/out ports
Secrets: distribution, parallelism
Composition Technique
Adaptation: filter around other components
Filter languages such as sed, awk, perl
Binding time: static
Composition Language
C, shell, tcl/tk, python …
Build management language makefile
Version management with sccs rcs cvs

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Components: classes
•   Objects are instances of classes (modules) with unique identity
•   Objects have runtime state
•   Late binding of calls by search/dispatch at runtime
Caller
Object  dispatch
Callee
Callee
Callee
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Component Model
Content: binary files, objects
(code and data)
Binding points: static (monomorphic) and polymorphic (dynamically dispatched) calls
Composition Technique
Adaptation by inheritance or delegation
Extensibility by subclassing
Composition Language

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CORBA / COM / .NET / EJB
•   Although different on the first sight, turn out to be rather similar
Caller
Object
(Client)
Callee
(Server)
Mediator
Software bus
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n   n   n
Language independent, location/distribution transparent interface definition language IDL source code or binary
Client
Java
Stub
Client
C
Stub
Interface specification
(in IDL) generate
Server
C++
Skeleton
Object adapter
Object Request Broker (ORB), Trader, Services

n   n
Microsoft’s model is similar to CORBA. Proprietary
(D)COM is a binary standard
Client
VBasic
COM stub
Client
C++
COM stub
Server
C++
COM skeleton
Server
C++
IDL skeleton
Object adapter
Monikers, Registry

n   n
Java only: source code / bytecode-based
Event-based, transparent distribution by remote method invocation (RMI – includes Java Object Serialization)
Bean
Java
Bean
Java
Bean
Java
Server
C++
IDL skeleton
Object adapter
Event InfoBus, RMI

n   n   n   n
Language independent, distribution transparent
NO interface definition language IDL (at least for C#) source code or bytecode MSIL
Common Language Runtime CLR
Client
Java
.net-CLR
Client
C#
.net-CLR
Server
C++
.net-CLR
CLR

Component Model
Content: binary components
Binding points are standardized
Described by IDL, set/get properties,
Standard interfaces (IUnknown...)
Secrets: distribution, language
Composition Technique
Adaptation for distributed systems
(marshalling) and mixed-language systems
(IDL)
Dynamic call in CORBA
VisualBasic for COM
Composition Language

n   n
Binding procedure is interpreted, not compiled
More flexible: n   n
When interface changes, no recompilation and rebinding
Ubiquitous http protocol – independent of a specific ORB
SOAP  interpretation
Caller
Object
Mediator
Callee
(Server)

Component Model
Content: not important
Binding points are described by XML
Binding procedure is interpretation of SOAP
Secrets: distribution, implementation language
Composition Technique
Adaptation for distributed systems
(marshalling) and mixed-language systems
Glue: WSDL, SOAP, HTTP
Dynamic discovery/binding with UDDI
Composition Language
BPEL
Web Services Business Process
Execution Language