Johns Hopkins University Software Engineering Fall 2002

1
Johns Hopkins UniversitySoftware
EngineeringFall 2002

• 5 November 2002
• Bill Akin

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Tonights Agenda

• Review the in-class exam
• Additional object-oriented concepts
• Architectures
• Infrastructures
• Analysis
• Modeling
• Requirements specification
• The revised schedule

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Definition

• An object is an entity or module that has a state
  and a defined set of operations to access and
  modify that state. (an old definition)
• We can also think of an object as a closed
  system, subsystem, or component that maintains
  its own state, accepts a specified set of
  messages (usually called methods), provides
  responses, and/or performs pre-defined functions.
• No external entity is able to see inside a
  correctly constructed object or directly control
  any of the objects internal processes.

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Methods, Operations, and Attributes

• Methods are the messages we send to objects that
  cause them to perform actions.
• Operations are the things we cant see that
  happen inside the objects to accomplish their
  defined actions.
• Attributes are the things an object knows about
  itself, e.g., its state data.
• Users of an object cannot see its operations or
  attributes.

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Concepts

• I have an abstract data class called CHECKING.
• I can create an object of that class and use it.
• Here are some methods
• PFCU.ESTABLISH as CHECKING with 1001
• PFCU.DEPOSIT 500
• PFCU.CHECK 25 Daily Times Herald
• print PFCU.BALANCE
• PFCU.REGISTER 1-January-2001 31-March-2001

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Applications

• I have an object-oriented air traffic control
  system.
• Here are some object concepts and methods
• RECEIVE_HANDOFF.3666R Denver
• SHOW.3666R
• PASS_HANDOFF.3666R Dallas
• SHOW_ALL FL3 FL6
• DISPLAY_SPEED.3666R
• DISPLAY_ETA.3666R VOR.Pecos
• DISPLAY_PILOT.3666R

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Special Object Uses

• Collaborative -- An object used in support of
  another object. A CHECKING object can use the
  services of a DATABASE object to maintain its
  state. This is hidden from the users of the
  CHECKING object.
• Guardian -- An object visible to the enterprise
  that provides the only available access to
  another resource.
• These two concepts can enable many objectives.

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Architecture

• Software architecture
• the structure of the components of a
  program/system, their interrelationships, and
  principles and guidelines governing their design
  and evolution over time.
• Definition from the SEI

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Architecture

• Architecture
• A minimal set of rules governing the arrangement,
  interaction, and interdependence of the parts or
  elements of a system whose purpose is to ensure
  that a conformant system satisfy a specified set
  of requirements.
• Identifies the services, interfaces, standards,
  their relationships.
• Provides the technical guidelines for
  implementation of systems upon which engineering
  specifications are based, common building blocks
  are built, and product lines are developed.
• Ingredients
• Rules Design Rules, Standards, Conventions
• Reference model(s)

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What is an Architecture?

• Definition The structure of components, their
  interrelationships, and the principles governing
  their design and evolution.
• Architecture types
• Operational
• Technical
• System

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Object-Oriented Architecture

• I will discuss the concept of object-oriented
  techniques applied to the development and
  maintenance of information processing
  architectures.
• I will outline the goals and objectives of the
  approach and the way I believe the objectives can
  be met.
• I will provide some simple examples of
  architecture level objects and discuss their
  implementation.

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Goals and Objectives

• Goals
• Improve the ability to maintain an information
  system, application, or enterprise
• Extend the useful life of an information system
• Enable inclusion and evolution of legacy elements
  in an information system
• Objectives
• Reduce the breakage for change requests
• Abstract system component implementation detail
• Shroud incorporated components

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Definition Information System

• An Information System is a set or arrangement of
  elements organized to accomplish some predefined
  goal by processing information.
• According to Fred Brooks, The hardest single
  part of building a software system is deciding
  what to build.No other part of the work so
  cripples the resulting system if done wrong. No
  other part is more difficult to rectify later.

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OO Architecture Classes
Client Class
DB Class

• An information system built on an object-oriented
  architecture has a set of classes, rules for
  using them, and an infrastructure that holds it
  all together.
• In the example we show two classes and an
  infrastructure.
• We can build a system using objects that are
  instances of the classes and plugging them into
  the infrastructure.

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Some Sample Classes

• User Application
• Server Application
• Archive Application
• Database Server
• Backup Server
• External Access Server

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OO Architecture Concept
DB-A
Client 2
Client 1
DB-D
DB-B
DB-C
New Client

• We could build a plug-and-play architecture.
• New databases can be plugged in.
• New Clients can be plugged in.
• It is a maintainable enterprise on a
  plug-and-play architecture.

New DB
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Example Object-oriented Architecture
User-II
Sys-B Data Manager
User-I
Sys-A Data Manager
Sys-B Backup
Security Admin
Sys-A Load Processor
Sys-C Data Manager
Audit Trail Archiver
Security Admin
Sys-B Load Processor
Loads Admin
Zip Data Manager
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Implementations

• Remember the objectives?
• Reduce the breakage for change requests
• Because state and process implementation are
  completely contained in an object, only the
  internal components are broken.
• Abstract(v) component implementation detail
• By definition all details of an object
  implementation are hidden.
• Shroud incorporated components
• Use guardian objects to own foreign components
  brought into a system.

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Global Resources

• Global resources should be treated as abstract
  objects.
• A guardian object should own such servers.
• As an example, consider a database to hold a
  companys inventory. The guardian is an object
  that advertises methods to its clients.
• Inside the guardian are commands understood by a
  small access database.
• If we change to oracle, only the guardian is
  modified, not the clients in our system.

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Technical Architecture

• Technical Architecture
• A minimal set of rules governing the arrangement,
  interaction, and interdependence of the parts or
  elements of a system whose purpose is to ensure
  that a conformant system satisfies a specified
  set of requirements.
• Identifies the services, interfaces, standards,
  their relationships.
• Provides the technical guidelines for
  implementation of systems upon which engineering
  specifications are based, common building blocks
  are built, and product lines are developed.
• Ingredients
• Rules Design Rules, Standards, Conventions
• Reference model(s)

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Information Infrastructure

• An information infrastructure is an integrated
  collection of elements based on technical
  architecture components that form the foundation
  on which functional components are supported
• An infrastructure may contain global resources
  available to all enterprise users
• Standard interfaces enable infrastructure use

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CII Concept of Operations
Internal
External
CII
Our Systems Outside the CII
Type III Applications
Type II Applications
Type I Applications
External Systems
Interoperability Services
Interoperability Services
Corporate Database (CD)
Pre-existing External Interfaces
CII Common Environment

• Infrastructure Services
• Hardware and Software Platforms

CII External Interfaces
Common Support Applications
Corporate Warehouse (CW)
Corporate Repository (CR)
COE
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CII Layers
CII Component A
CII Component B
Virtual Connection
Request
API
Response
Request
API
Response
Request
Response
Request
Response
COE APIs
COE APIs
Request
Response
Request
Response
Interfaces
Interfaces
Actual Connection
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Context
Client
Server
Virtual Connection
Layer - 1
Layer - 1
1 - PDU
Layer - 2
Layer - 2
2 - PDU
Layer - 3
Layer - 3
3 - PDU
Layer - 4
Layer - 4
4 - PDU
Common Operating Environment (COE)
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Anatomy of a Layer
N service primitive (request or response)
N service primitive (confirm or indication)
Layer-N
N-1 service primitive (request or response)
N-1 service primitive (confirm or indication)
Terms
SAP Service Access Point SDU Service Data Unit
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Anatomy of a Layer External View
N service primitive (request or response)
N service primitive (confirm or indication)
Layer-N
N-SAPs
Term
SAP Service Access Point
N-SAPs
N-1 service primitive (request or response)
N-1 service primitive (confirm or indication)
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Anatomy of a Layer Internal View
N-SAPs
Layer-N
Term
SAP Service Access Point
N-Service Entity
N-SAPs
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Analysis and Modeling

• Data modeling specify all data produced or
  consumed by the system
• Functional modeling and information flow all
  data flows and related functional processes
• Behavioral Modeling state transition diagrams
  or finite state machines
• User interface uses and use cases or other
  prototyping models
• Now lets work an example together

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Specify Requirements

• Identify major, intermediate, and minor
  functional views and elements
• Break a document into their boundaries
• Write a descriptive narrative at each level
• At the lowest (minor) level write all the
  requirement statements that specify that element
• Each requirement statement is either a capability
  or a constraint.
• Now lets expand our example

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Where are we

• Six class meetings left including tonight
• Project needs to be completed, demonstrated, and
  delivered
• Several topics left to be covered, including
• Design
• Testing
• SCM
• SQA
• Component-based design
• Additional object-oriented techniques

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Schedule

• Class Date Chapters Events and Deliveries
• 10 12-Nov 8, 9, 24 Deliver requirements
  document
• 11 19-Nov 17, 18 High Level Design Presentation
• 12 26-Nov Deliver high level design document
• 13 3-Dec Final Exam
• 14 10-Dec Project Demonstrations - Deliver
  project