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CAD SOFTWARE
ME C382: COMPUTER AIDED DESIGN
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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
I/C: Dr. Regalla Srinivasa Prakash, Mechanical Engg., B. I. T. S., Pilani 3
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
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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
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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
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X4 Y4
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Database ModelsDatabase Models
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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Database ModelsDatabase Models
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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Database ModelsDatabase Models
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
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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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Database ModelsDatabase Models
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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Database ModelsDatabase Models
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
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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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