2 cadsoftware programming

7/31/2019 2 Cadsoftware Programming

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CAD SOFTWARE

ME C382: COMPUTER AIDED DESIGN

I/C: Dr. Regalla Srinivasa Prakash, Mechanical Engg., B. I. T. S., Pilani 1


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T ical Learnin Curve

Graphics Standards Basic Definitions Modes of Graphics Operations

User Interface Modeling and Viewing Software Documentation Software Development Efficient use of CAD Software



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Typical Learning Curve for CAD

Knowled e

Gained

STEEP CURVE

Furthertraining

andmastering

Confusionzone: slowlearning, not

Mastering

the


TimeInitial learning period


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Data Structure

data items or elements that are related to eachother by a set of relations.

In CAD/CAM, a data structure is a scheme,logic, or sequence of steps to achieve graphics,non-graphics or programming goal

Three different types of data structures for CAD:

Based on Edges

Based on Vertices Based on Blocks



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Database

It may be defined as an organized collection of graphicsand non-graphics data stored on secondary storage inthe computer.

storage s that it will be available for operations anddecision making.

requirements:

Eliminate redundancy: both design and manufacturing

Enforce standards: data interchange and migration becomeseasy

Maintain integrity: for accuracy and consistency

Balance conflicting requirements: aim at overall besterformance for exam le both desi n and manufacturin not


either alone


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POPULAR CAD DATABASE MODELS

Hierarchical database

etwor ata ase

Object oriented database



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Database ModelsDatabase Models Relational Database Model

Background

E. F. Codd developed the relational model in 1970. Conceptually simple but versatile

Requires more computing power Considered impractical in the 1970s

Modern computers (even PCs) are powerful enough tohandle relational databases.



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Database ModelsDatabase Models

Relational Database Model

Basic Structure

Relational DataBase Management System(RDBMS)

e a ona a a ase s perce ve y e user as acollection of tables in which data are stored.

Each table consists of series of row/column intersections. Tables (or relations) are related to each other by sharing

a common entity characteristic.

The relationship type is often shown in a relational

schema. A table yields complete data and structural

independence because it is a purely logical structure.



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Database ModelsDatabase Models e a ona a a ase o e



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Point X Y

Surface

Line/Curv

Type

1 X1 Y12 X Y

Line StartPoint

Endpoint 1 A Line

3 X3 Y3A 1 4

B 1 2

ne

C Line

4 4

5 X5 Y5

C 2 3

D 3 4

D Line

2 E Line6 X6 Y6

7 X7 Y7E 5 6 F Line

G Line

8 X8 Y8Relation POINT

G 7 8Relation

D Line

Relation


LINE/CURVE SURFACE


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Database ModelsDatabase Models Relational Database Model

Advantages

Data independence and structural independence Easy to design the database and to manage its

contents

Less programming effort required

Structured Query Language (SQL)

Fourth Generation Language (4GL)

Specify what to do not how to do Introduced by IBM in 1974



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Disadvantages

and operating system overhead.

It tends to be slower than other

database systems.



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Background

was developed by North American Rockwell to

simplify parts inventory management for the Apollopro ect.

Information Management System (IMS) -- Jointly

Data records are organized in an inverted (upside-down) tree structure -- hierarchical structure.



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Object (root)

S1 S2 Surface level

A B C D E F G DEdge level

1 4 3 4 5 6 3 4

Vertex

level

X1 Y1 X4 Y4 X5 Y5

Coordinate

level


X4 Y4


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Basic Structure

upside-down tree structure. One-to-Many (1:M) Relationship

.

Each child has only one parent.

Example:

computers storage media.

Preorder (Top down) traversal-more popular

With preorder traversal frequently accessed segments areplaced close to the left side of the tree to minimize access


.


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Advantages

Data independence -- Reduced programming and

maintenance effort Database integrity- a child must have a parent

Efficiency dealing with a large database containing

a a w pre om nan y : re a ons ps - manybusiness applications fall in this category



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Hierarchical Database Model

Disadvantages

Requirement of knowledge of physical level of data storage

Inability to represent relationships that do not conform to thehierarchical 1:M standard

Applications programming is complex - programmer mustknow the database structure and how to traverse it

Lack of ad hoc uer ca abilit for end users

Lack of standard concepts and implementation (No standardwas developed)-- limited portability

database - Most serious problem



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Background

created DataBase Task Group (DBTG) in 1971 to developstandards for a database environment.

Network schema defines the conceptual organization of the

entire database as viewed by the database administrator.

Subschema defines the ortion of the database as seen b theapplications programs.

Data Management Language defines the data characteristicsand the data structure and to manipulate the data.



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Database ModelsDatabase Models Network Database Model

Background

ree ata management anguage components:

Schema Data Definition Language (DDL) - used by DBA todefine schema components

u sc ema a a e n on anguage - use y app ca onprograms to define part of the schema to be used by theprogram

-

database contents

ANSI SPARC (Standards Planning And RequirementsCommittee au mented the database standards in 1975.

A popular network DBMS is Computer Associates IDMS/R



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e wor a a ase o eBasic Structure

et -- A relationship is called a set. Each set is

composed of at least two record types: an ownerarent record and a member child record.



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Network Database Model Relationships among the records are decomposed

.



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1 2

Surface level

A B C D E F GEdge level

1 2 3 4 5 6 7 8Vertex level



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Advantages

More flexible data access compared to

Hierarchical model - An application can access anowner and all the members within the set, one canalso access owner from a member.

-defined before defining member records

Data independence through the DBMS



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Disadvantages

programmers point of view

Difficult to design and use properly - because ofthe navigational nature of the data structure

Difficult to make changes in a database - no



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Database Models

OO Database Model

Objects are abstractions of real-world entities

Example: Student, Invoice, Employee Objects capture both attribute and behavior

(methods)

Objects with similar characteristics aregrouped together as a class

Classes are organized in a class hierarchy

A subclass inherits the attributes and methodsfrom its superclass



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Advantages -

attributes, methods, and class hierarchies

Useful in niche application areas such asCAD/CAM

Disadvantage

Data access method resembles the navigationalstyle



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OBJECT

SUB-OBJECT B1 SUB-OBJECT B2



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ADDITIONAL ADVANTAGES FROM

Multiple engineering applications fromconce tual desi n to manufacturinoperations

Dynamic modification and extension of the



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.

is not common in business data.

a a ase managemen sys emsmust support the tentative, iterative and

evo u onary na ure o e es gn process.



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.

for storage and management of multiple

particular design.

There is seldom a unique solution to a

optimal solutions.



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supported from the database.

Large design projects usually multiplees gners wor ng s mu aneous y onmultiple aspects of a project



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.

ue to t e terat ve nature o es gn,

earlier generated data may not becomm e o e a a ase un e es gnprocess is completed.



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.

e ata ase system s ou not mpose

constraints on the designer to followecause eren es gns requ re erensequences.



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.

Application program requiring data from a

extensive knowledge of the database.

This is important in customizing CAD

sys ems or spec c es gn anmanufacturing procedure.



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Easy to work with

Have its own embedded programming language

Be compatible with other CAD/CAM and


Major Benefits of a CAD package


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Major Benefits of a CAD package

Automates repetitive tasks

reduces duplicate efforts

Allows you to communicate with others viaelectronic means

Makes drawing revisions easier to perform

Enable you to customize environment Lets you to create accurate and high-quality

drawing

Provides impressive presentation Supports a wide selection of hardware



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