Structured Logic Design With Very Higspeed Integrated Circuit Hardware Description Language

This presentation explains Structured Logic Design With Very Higspeed Integrated Circuit Hardware Description Language

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Overview -Design
•Introduction to Design
•Review of Architectural Design
•Modules
•Structured Design
•Objects
•Object-Oriented Design
•Detailed Design
•Integration Testing

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Goals and Objectives
•Develop a coherent representation of a software system
that will satisfy the requirements
•Identify inadequacies in the requirements
•Develop review plan that demonstrates coverage of the
requirements
–yields confidence in design
•Develop test plan that covers design
–yields confidence in both design and implementation

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Introduction to Design
Requirements
Change
Validation
Revalidation
Validation
Verification
Testing
Requirements Analysis +
Specification
Design
How ?
Operation and
Maintenance
Implementation and
Integration

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Relationship to other lifecycle phases
•Requirements
–Specifies the “what” not the “how”
–Provides conceptual boundaries
¤keeps design focused
•Implementation
–Design stops and coding begins when design specifications are
sufficient for coding assignments
¤each assignment, theoretically, can be given to a programmer unaware of
the overall system architecture

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Basic Design Process
•The design process develops several models of the
software system at different levels of abstraction
–Starting point is an informal “boxes and arrows” design
–Add information to make it more consistent and complete
–Provide feedback to earlier designs for improvement
Informal
design
outline
Informal
design
More formal
design
Finished
design

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Top-Down Design
•Recursively partition a problem into sub-problems until
tractable (solvable) problems are identified
System level
subsystem
level
module level

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Design Activities
•Architectural design
–Subsystem identification
¤services and constraints are specified
–Module design
¤modular decomposition is performed; relationships specified
•Detailed design
–Interface design
¤module interfaces are negotiated, designed and documented
–Data structure and algorithm design
¤module details (data structures and algorithms) to provide system
services are specified

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Design Products
•Refined requirements specification
•Description of systems to be constructed
–software architecture (diagram)
–modular decomposition (hierarchy)
–abstract module interface specifications
–detailed module designs
•Documentation of decisions and rationale
•Data dictionary of all defined objects
•Validation review plan
•Integration test plan

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Desirable Characteristics/ Common Problems
•Uniform
•Complete
•Rigorous
•Confirmable, verifiable,
testable
•Supportable by tools
•Desensitized to change
•Accommodates independent
coding
•Depth-first design: only
partial satisfaction of
requirements
•Failure to consider potential
changes
•Too detailed: overly
constrains implementation
•Ambiguous: misinterpreted
during implementation
•Undocumented: designers
become essential
•Inconsistent: system cannot
be integrated

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Architectural Design
•Architectural Design
–decomposition of large systems that provide some related set of
services + establishing a framework for control and
communication
•Architectural styles establish guidelines
–a relatively new area of research
•No generally accepted architectural design process
–some important sub-processes
¤System structuring: structuring of the system into a number of
subsystems, where a subsystem is an independent software unit
¤Control modeling: establishing a general model of control relationships
between the parts of the system
¤Modular decomposition: decomposing each identified subsystem into
modules

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Software Architecture
•Components
–The elements out of which the system is built
–Examples: filters, databases, objects, ADTs
•Connectors
–The interaction or communication mechanisms
–The glue that combines the components
–Examples: procedure calls, pipes, event broadcast, messages,
secure protocols
•Constraints
–Limitations on the composition of components and connectors

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Architectural Style
•Example architectural styles
–Batch sequential
–Pipe and filter
–Main program and subroutines
–Blackboard
–Interpreter
–Client-server
–Communicating processes
–Event systems
–Object-oriented
–Layered Systems
Families of systems defined by patterns of composition

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Architectural Design:
System Structuring
•Model of the system structure and decomposition
¤how subsystems share data
¤how they are distributed
¤how they interface with each other
•Three standard models
–Repository model:how subsystems exchange and share information
•E.g., all shared data is held in a central database or each sub-system maintains its
own database
–Distribution model:how data and processing is distributed across a range of
processors
•E.g., Client-server or peer-to-peer processes
–Abstract machine model:the interfacing of subsystems as abstract machines
each of which provides a set of services to others
•E.g., each subsystem defines an abstract machine

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Architectural Design:
Control Modeling
•Control of subsystems so that services are delivered to the
right place at the right time
•Two general approaches
–Centralized control
¤One subsystem has overall responsibility for control and starts/stops
other subsystems
•call-return model (sequential)
•manager model (concurrent)
–Event-based control
¤each subsystem responds to externally generated events (from other
subsystems or the environment)
•broadcast model
•interrupt-driven model

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Architectural Design:
Modular decomposition
•After decomposition of the system into subsystems,
subsystems must be decomposed into modules
–No rigid distinction between system and modular decomposition
•Two important approaches for decomposing subsystems
into modules:
–Data-flow (structured design)
¤system is decomposed into functional modules which accept input data and
transform it to output data
¤process-based decomposition
¤achieves mostly procedural abstractions
–Object-oriented (object-oriented analysis and design)
¤system is decomposed into a set of communicating objects
¤object-based decomposition
¤achieves both procedural + data abstractions

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Architectural Design:
Hierarchy
•Hierarchies support modular decomposition
–Uses relation:auses bonly if the correct functioning of a
depends on the existence of a correct implementation of b
¤modular decomposition can be specified by uses, where
•Level 0 is the set of all programs that use no other program
•Level i (i> 0) is the set of all programs that use at least one program on
level i-1 and no program at level ≥ i.
•Note: the usesrelation does not always provide a hierarchy
–Is-composed-of relation: a is-composed-of bif b is a
component of aand encapsulated within a
¤modular decomposition can be specified by is-composed-of, where
•non-terminals are virtual code
•terminals are the only units represented by code
•Then, the usesrelation is specified over the set of terminals only
•Note: the is-composed-of relation is acyclic

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Modules
•Definition: a software entity encapsulating the
representation of an abstraction and providing an abstract
interface to it
•Module interaction
–Module hides implementation details so that the rest of the system is
insulated and protected from the details AND vice versa
–Modules communicate only through well-defined interfaces
•Negotiating module interfaces
–design interface to component to be insensitive to change
–determine likely usage patterns and purposes
–disseminate minimal information as useful generalities
¤abstract Interfaces: one specification, many possible implementations
–suppress unnecessary detail of a design decision

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Architecture, Subsystems and Modules
•Architecture consists of interacting subsystems
–determined by application domain
•Subsystems
–a component whose operation does not depend on the services
provided by other subsystems
–communicates with other subsystems via defined interfaces
–is decomposed further into modules by design methods
•Modules
–a component that provides one or more services to other
modules
–not normally considered an independent subsystem

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Modular Decomposition:
Abstraction
•Abstraction is a tool that supports focus on important, inherent
properties and suppression of unnecessary detail
–permits separation of conceptual aspects of a system from the
implementation details
–allows postponement of design decisions
•Three basic abstraction mechanism
–procedural abstraction
¤specification describes input/output
¤implementation describes algorithm
–data abstraction
¤specification describes attributes, values, properties, operations
¤implementation describes representation and implementation
–control abstraction
¤specification describes desired effect
¤implementation describes mechanism

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Modular Decomposition:
Information Hiding
•Information hiding is a decomposition principle that requires that
each module hides its internal details and is specified by as little
information as possible
–forces design units to communicate only through well-defined interfaces
–enables clients to be protected if internal details change
•Sample entities to encapsulate
–abstract data types
–algorithms
–input and output formats
–processing sequence
–machine dependencies
–policies (e.g. security issues, garbage collection, etc.)

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Modular Decomposition:
Cohesion and Coupling
•Cohesion
–the degree to which the internals of a module are related
•Coupling
–the degree to which the modules of a design are related
•The ideal system has highly cohesive modules that are
loosely coupled
–high cohesion -> well-designed reusable module
–low coupling -> coherent design, resistant to change

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Types of Cohesion
•coincidental
–multiple, completely unrelated actions
•logical
–series of related actions, often selected by parameters
•temporal
–series of actions related in time
•procedural
–series of actions sharing sequence of steps
•communicational
–procedural cohesion but on the same data
•informational
–series of independent actions on the same data
•functional: exactly one action
(Good)
(Bad)

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Types of Coupling
•content
–one module directly references content of another
•common
–both modules have access to same global data
•control
–one module passes an element of control to another
•stamp
–one module passes a data structure to another;
which only uses part of the passed information
•data
–one module passes only homogeneous data items
(Good)
(Bad)

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Some examples of cohesion
•Logical cohesion
–Input/Output libraries
–Math libraries
•Temporal cohesion
–Program initialization
•Communicational cohesion
–“calculate data and write it to disk”
–Closely related: sequential cohesion
¤the output of one element is the input to another

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Some examples of coupling
•Control coupling
–One module passes control flags (parameters or global
variables) that control the sequence of processing steps in
another module
•Stamp coupling (alternative definition)
–Similar to common coupling (modules that share global data)
except that globals are shared selectively among routines that
require the data
–Ada packages support stamp coupling since variables defined in
a package specification are shared between all modules which
use the package.

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Structured Design
•System is completely specified by the functions that is to
perform
–Top-down, iterative refinement of functionality
¤break the [system] function into subfunctions
¤determine hierarchy and data interaction
–Function refinement guides data refinement
–Hierarchical organization is a tree with one module per subfunction
•Pros and Cons
–modules are highly functional
–best suited when state information is not pervasive
–data decisions must be made earlier
–changes in data ripple through entire structure
–little chance for reusability

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Structured Design Process
•Identify flow of data and incorporate detail and structure
iteratively
–given specification loop
¤identify data flow and transformations
•nouns as data, verbs as transformations
¤derive data flow diagrams
¤identify "natural aggregates"
•identify highest level input and output units
•remaining units are central transforms
•form level of structure chart
•control module (coordinate)
–input module (afferent)
–central module(s) (transform)
–output module (efferent)
•form structure chart
–until implementation is immediate

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Data Flow Diagrams
•Software system as flow of data from logical
processing unit A (transformation) to B
–do not include control information
–data flow diagram elements
¤round-cornered rectangle = transformation
¤vector = data flow
¤vector operation = data flow link
•* (and)
•+ (or)
•+ (exclusive or)
¤arc with data flow link = bracketing to override precedence
•and over or over exclusive or
¤rectangle = data store
¤circle = user interaction (input/output)

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Data Flow Templates+
+
*
A
A
A
B
B
B
C
C
C
conjunct
disjunct
exclusive *
+
+
A
A
A
A
B
C
B
B
C
C
C
simple
conjunct
disjunct
exclusive

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Structure Charts
•Depict software structure as a hierarchy of modules
and data communication
–may have control info defining selection and loops
–structure chart elements
¤rectangle = module
¤four types of module based on data flow
•control (coordinate)
•input (afferent)
•central (transform)
•output (efferent)

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Structure Charts (cont’d)
¤vector = control relationship
¤arrow with circular tail = directed data relationship
•data couple (open), control couple (closed)
¤round-cornered rectangle = data store
¤circle = user interaction (input/output)

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Structure Chart TemplatesCOORDINATETRANSFORM
AFFERENT EFFERENT
X
X
A B
Z
Z
D D

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Overview -Object-Oriented
Analysis and Design
•Introduction to OOAD
•Introduction to Objects
–Background
–Object-Oriented Programming
–Classes and Objects
–Object-Oriented Concepts
•Object Modeling Technique
–Object-Oriented Analysis
–Object-Oriented Design

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Object-Oriented Approaches
•Object-Oriented Methodology
–development approach used to build complex systems using the
concepts of object, class, polymorphism, and inheritance with a
view towards reusability
–encourages software engineers to think of the problem in terms
of the application domain early and apply a consistent approach
throughout the entire life-cycle
•Object-Oriented Analysis and Design
–analysis models the “real-world” requirements, independent of
the implementation environment
–design applies object-oriented concepts to develop and
communicate the architecture and details of how to meet
requirements

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General Advantages
•Understandable
–maps the “real-world” objects more directly
–manages complexity via abstraction and encapsulation
•Practical
–successful in real applications
–suitable to many, but not all, domains
•Productive
–experience shows increased productivity over life-cycle
–encourages reuse of model, design, and code
•Stable
–changes minimally perturb objects

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Advantages wrt“Principles”
•Separation of concerns
–developers focus on common versus special properties of objects
•Modularity
–specifically in terms of classification of objects
•Abstraction
–allowing common versus special properties to be represented separately
•Anticipation of change
–new modules (objects) systematically specialize existing objects
•Generality
–a general object may be specialized in several ways
•Incrementality
–specific requirements (e.g. performance) may be addressed in
specializations

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Object-oriented versus Classical
SW development
Object-oriented
Analysis
Object-oriented
Design
Object-oriented
Implementation
Maintenance
Requirements
Analysis
Design
Implementation
& Integration
Maintenance

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Background -Objects
•Traditionally, programming has been
“procedure-oriented”
–Focus on process, algorithms, and tools
–A system’s data has secondary importance
•Data and process considered separate
–The data is external to a program; a program reads it in,
manipulates it, and then writes it out
–Relationships between data types not considered important
¤As a result, similarities were not leveraged leading to duplication of code

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Background, continued
•Problems
–Lack of data encapsulation
¤changes to a data format typically required major rewrites
–Poor models
¤Real world entities not well represented in requirements, design and
implementation
•If an assumption about an entity changes, multiple modules may have to
change in response (since logic about an entity may be spread across
modules)
–Low reuse
¤Procedure-oriented modules are often difficult to reuse outside of their
original development context

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Object-Oriented Programming
•Objects combine both data and process
–Increases the stature of data to be equivalent to process
•Focus on real-world entities
–Objects often represent real-world counterparts: people,
countries, calendars, cars, organizations, etc.
•Enables Categorization
–Objects with high levels of abstraction can often be specialized
to more specific categories
¤For instance, car Honda Civic
¤or person athlete soccer player

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Object-Oriented Programming, continued
•Addresses “Procedure-Oriented” Problems
–Data and Process encapsulation
¤Encapuslates data and related algorithms behind a single interface; both
can be evolved without affecting other objects or modules (as long as the
interface is constant)
–Natural Models
¤Objects can be used to appropriately structure a design or accurately
create a set of requirements based on knowlede about the real-world
counterpart
–Increased Reuse
¤Well-designed object is often independent of the original development
context

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Object name
state
(attributes)
access to attributes
Method 1
Method 2
Method 3
Objects
•Data and operations are defined as a single unit
•Object :=
–encapsulated state (attributes)
–methods that exclusively control access to the state

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Classes
•Each object is an instance of a class
•A class serves as a blueprint
–It defines the attributes and methods for the class
–Thus, each object of a class has exactly the same interface and
set of attributes
¤each object can have different values for its attributes
Professor
Name: string
Dept: string
get_name()
return string
....
class Professor
(Professor) (Professor)
Jean Raoul
French
Debra Richardson
ICS
get_name()
....
get_name()
....
Object instances of Professor

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Object Model Notation: Introduction
Class Name
(Class Name)
InstanceVariable1
InstanceVariable2: type
InstanceVariable1 = value
InstanceVariable2: type
Method1()
Method2(arguments) return type
Method1()
Method2(arguments) return type
Classes are represented as rectangles;
The class name is at the top, followed by attributes
(instance variables) and methods (operations)
Depending on context some information can be
hidden such as types or method arguments
Objects are represented as rounded rectangles;
The object’s name is its classname surrounded by
parentheses
Instance variables can display the values that they
have been assigned; pointer types will often point
(not shown) to the object being referenced

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Object Communication
•Objects communicate via method invocation
–This is known as message passing
–Legal messages are defined by the object’s interface
–This interface is the only legal way to access another object’s
state
(Rectangle)
get_width
get_height
calculate_area
width
height
Object

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Objects: Terminology (partial review)
•Class
–set of objects having the same methods and attributes
–has a specification and an implementation
–behavior is defined by the operations that can be performed on
objects belonging to the class
•Method
–action that can be performed on any member of a class
•Encapsulation
–packaging the specification and implementation of a class so
that the specification is visible and the implementation is hidden
from clients
•Instantiation
–the creation of a new object belonging to a class

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Objects: Terminology, continued
•Aggregation
–Objects representing components are associated with an object
representing their assembly (e.g. consists-of)
–A mechanism for structuring object models
Weather
mapping system
Weather
station
Map
database
Weather
map
consists of

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Aggregation: example
consists of
consists of
Microcomputer
Monitor System box Mouse Keyboard
Chassis CPU RAM Fan

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Objects: Terminology, continued
•Generalization
–Allows a class, called a supertype, to be formed by factoring out the
common state and methods of several classes, called subtypes (is-a)
–Specialization is the converse case
Course
title
Undergrad Course
length
Postgrad Course
level
is-a
Supertype
Subtypes

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Generalization: example
Dog Cat
Animal
is-a
Enables the creation of lists which
can consist of elements with
different types!
animalList: listOf(Animal)
animalList Cat Animal Dog

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Aggregation/ Generalization: example
consists of
consists of
Microcomputer
Monitor System box
Mouse Keyboard
Chassis CPU RAM Fan
Input Device
is-a
Color Monitor B/W Monitor
is-a
Specialization
Generalization

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Objects: Terminology, continued
•Inheritance
–a subclass inherits methods and attributes from its superclass; a subclass can
also add additional operations and attributes;
–e.g.: subclasses Undergrad Course and Postgrad Course inherit the title
attribute from the superclass Course
•Class hierarchy
–generalization and inheritance are transitive across the hierarchy
–e.g. vehicle->automobile->4-door->Suburu Legacy; the legacy inherits from
4-door, automobile, and vehicle
•Multiple Inheritance
–subclass inherits operations and attributes from more than one superclass
(not a strict hierarchy)

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Class Hierarchy -Single Inheritance: example
is-a
is-a
is-a
is-a
Vehicle
LandVehicle WaterVehicle AirVehicle
truckcar
sailboat
airplane helicopter
motorboat ship yatch

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Class Hierarchy -Multiple Inheritance: example
is-a
is-a
Vehicle
is-a
LandVehicle WaterVehicle
Car
Amphibious
Vehicle
Boat

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Polymorphism
•A superclass defines an operation which its subclasses
override.
•Via generalization a client may have a variable of the
superclass type which is pointing to an instance of the
subclass.
•When the operation is called, the subclass’s
implementation is invoked

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Polymorphism: example
is-a
is-a
Vehicle
is-a
LandVehicle WaterVehicle
Car
Amphibious
Vehicle
Boat
defines methods
turnOn() and
turnOff()
Each subclass implements turnOn() and turnOff()

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Polymorphism: example, continued
myVehicle: Vehicle := new Boat();
myVehicle->turnOn();
myVehicle->turnOff();
•In both cases, its Boat.turnOn() and Boat.turnOff() that’s
executed!

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Good and poor object classes
Discussion
•Reasonableness of an object depends on the
problem at hand: the challenge of O-O analysis is to
find relevant object classes
¤Country: USA, Australia
¤State: California, Washington
¤Thermometer
¤Temperature: 32°F
¤Computer file
¤Swimming
¤Students
¤Class of students
¤Students whose middle initial is J
¤Inventory
¤Automobile Part
¤Part ID