DATABASE APPLICATION DEVELOPMENT SAK 3408 Database Design I (week 2)
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Transcript of DATABASE APPLICATION DEVELOPMENT SAK 3408 Database Design I (week 2)
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DATABASE APPLICATION DEVELOPMENTSAK 3408
Database Design I(week 2)
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SAK3408 by PSS (W2)
REMEMBER
Des
ign
SQ
L
Pro
gram
Best:
Spend your time
on design and SQL.Des
ign
SQ
L
Pro
gram
Worst:Compensate for poor designand limited SQL with programming.
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Database System Design
User viewsof data.
Conceptualdata model.
Customer(CustomerID, Name, Address, …)
SalesPerson(EmployeeID, Name, Commission, … )
Order(OrderID, OrderDate, CustomerID, EmployeeID, … )
OrderItem(OrderID, ItemID, Quantity, Price, … )
Item(ItemID, Description, ListPrice, …)
Implementation(relational)data model.
Physicaldatastorage.
Class diagram that shows business entities, relationships, and rules.
List of nicely-behaved tables. Use data normalization to derive the list.
Indexes and storage methods to improve performance.
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The Need for Design Goal: To produce an information system
that adds value for the user Reduce costs Increase sales/revenue Provide competitive advantage
Objective: To understand the system To improve it To communicate with users and IT staff
Methodology: Build models of the system
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Designing Systems
Designs are a model of existing & proposed systems They provide a picture or
representation of reality They are a simplification Someone should be able to read your
design (model) and describe the features of the actual system.
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How to builds your model?
You build models by talking with the users Identify processes Identify objects Determine current problems and future
needs Collect user documents (views)
Break complex systems into pieces and levels
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Initial Steps of Design
1. Identify the exact goals of the system.
2. Talk with the users to identify the basic forms and reports.
3. Identify the data items to be stored.
4. Design the classes (tables) and relationships.
5. Identify any business constraints.
6. Verify the design matches the business rules.
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Design Stages
Initiation Scope Feasibility Cost & Time estimates
Requirements Analysis User Views & Needs
Forms Reports
Processes & Events Objects & Attributes
Conceptual Design Models
Data flow diagram Entity Relationships Objects
User feedback
Physical Design Table definitions Application development
Queries Forms Reports Application integration
Data storage Security Procedures
Implementation Training Purchases Data conversion Installation
Evaluation & Review
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Overview of Database Design Process
REQUIREMENTS COLLECTION & ANALYSIS
Data requirement
CONCEPTUAL DESIGN
Conceptual Schema
LOGICAL DESIGN(DATA MODEL MAPPING)
Logical SchemaIn the data model of specific DBMS
PHYSICAL DESIGN
Internal Schema
Functional Requirements
FUNCTIONAL ANALYSIS
APPLICATION PROGRAM DESIGN
TRANSACTION IMPLEMENTATION
High-Level Transaction Specification
Application Program
DBMS-independentDBMS-specific
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Unified Modeling Language (UML)
A relatively new method to design systems.Contains several types of diagrams:
Contains several types of diagrams:
The class diagram is the most important for database design.
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Definitions
Entity: Something in the real world that we wish to describe or track.
Class: Description of an entity, that includes its attributes (properties) and behavior (methods).
Object: One instance of a class with specific data.Property: A characteristic or descriptor of a class or entity.Method: A function that is performed by the class.Association: A relationship between two or more classes.
Entity: Customer, Merchandise, SalesClass: Customer, Merchandise, SaleObject: Joe Jones, Premium Cat Food, Sale #32Property: LastName, Description, SaleDateMethod: AddCustomer, UpdateInventory, ComputeTotalAssociation: Each Sale can have only one Customer.
Pet Store Examples
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Business Rule
BR are important in data modelling because they govern how data are – handled and stored.
Basic BR : Data names Data definition
Names and definition must provide for : Entity types Attribute Relationship
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Guideline Data Names
Relate to business – customer \ File10
Be meaningful – avoid is, it, has Be unique – homeadd, campusadd Repeatable–studbirthdate,
stafbirthdate
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Data Definition
“ A course is a module of instruction in a particular area.”
“A customer may request a model car from a rental branch in a particular date.”
Guideline : A definition will state such characteristics of
the data objects. Whether the data is singular or plural Who determine the value for the data Whether data is static or changes over time Whether the data is optional or an empty Where, when and how data is created.
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The E-R Model
E-R model – a logical representation of the data for an organization or for a business area
E-R diagram – a graphical representation of an entity-relationship model
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E-R Model Constructs
EntityAttributeRelationship
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Basic E-R Notation
Entity symbols
Relationship symbols
Attribute symbols
A special entity that is also a relationship
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Figure 2.3 Sample E-R Diagram
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Entity
An entity is a person, place, object, event or concept in the user environment about which the organization wishes to maintain data.
Ex: Person – EMPLOYEE, STUDENT, PATIENT Place – STORE, WAREHOUSE, STATE Object – MACHINE, BUILDING, AUTOMOBILE Event – SALE, REGISTRATION, RENEWAL Concept – ACCOUNT, COURSE
Entity type, entity instances, strong entity, weak entity
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Entity Type vs. Entity Instance
Entity Type Share common characteristic Given a name (CAPITAL LETTER) Rectangle Collection of entities (often corresponds to a
table). Ex: EMPLOYEE
Entity Instances a single occurrence of an entity type (often
corresponds to a row in a table) Ex: may be 100 of instances of entity
EMPLOYEE stored in database.
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Entity Type vs. Entity Instance (cont.)
Entity Type : EMPLOYEE
Attribut : EMP_NUM CHAR(10)NAME CHAR(25)STATE CHAR(35)
2 instances of EMPLOYEE :00123 02345Ali AmirPerak Kedah
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Strong vs. Weak Entity Types
Strong Entity Type entity that exists independently of other entity
types Unique characteristic Called an identifier Ex: STUDENT, EMPLOYEE
Weak Entity Type entity type whose existence depends on
some other entity type No meaning in ERD without strong entity.
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Figure 2.10 Strong and weak entities
Strong entity Weak entityIdentifying relationship
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Attribute property or characteristic of an entity
type (often corresponds to a field in a table)
Ex: entity type – STUDENT Attributes – name, add, id, program
Simple att vs composite att. Single-valued att vs multivalued att Stored att vs derived att Identifier att.
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Example
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Simple vs. Composite Attribute
Simple attribute – cannot broken into smaller components
Composite attribute – can broken into component parts
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Simple key attribute
The key is underlined
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a) Composite attribute
An attribute broken into component parts
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b) Composite key attribute
The key is composed of two subparts
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Single-Valued vs. Multivalued Attribute
Single-Valued – each of the attributes has one value
Multivalued – attribute more than one value
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Entity with a multivalued attribute (Skill)
Multivalued: an employee can have more than one skill
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Stored vs. Derived Attributes
Stored attribute – data input or set
Derived Attribute – attribute whose values can be calculated from related attribute values.
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Entity with a derived attribute (Years_Employed)
Derived from date employed and current date
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Identifiers (Keys)
Identifier (Primary Key) - An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type
Composite Identifier – an identifier that consists of a composite attribute.
Candidate Key – an attribute that could be a key…satisfies the requirements for being a key
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Characteristics of Identifiers
Will not change in value Will not be null No intelligent identifiers (e.g.
containing locations or people that might change)
Substitute new, simple keys for long, composite keys
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Ex: identifier
The key is composed of two subparts
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Relationship
Relationship link between entities (corresponds to
primary key-foreign key equivalencies in related tables)
Relationship Types vs. Relationship Instances The relationship type is modeled as the
diamond and lines between entity types…the instance is between specific entity instances
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Relationships (cont.)
Relationship Types vs. Relationship Instances
The relationship type is modeled as the diamond and lines between entity types…the instance is between specific entity instances
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Figure 2.6 (a) Relationship type
Figure 2.6 (b) Entity and Relationship instances
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Relationships (cont.)
Relationships can have attributes These describe features pertaining to the
association between the entities in the relationship
Two entities can have more than one type of relationship between them (multiple relationships)
Associative Entity = combination of relationship and entity
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Degree of Relationships Degree of a Relationship is the
number of entity types that participate in it Unary Relationship Binary Relationship Ternary Relationship
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Figure 2.7 Degree of relationships
One entity related to another of the same entity type
Entities of two different types related to each other
Entities of three different types related to each other
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Cardinality of Relationships
One – to – One Each entity in the relationship will have
exactly one related entity One – to – Many
An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity
Many – to – Many Entities on both sides of the relationship can
have many related entities on the other side
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Figure 2.8 Degree of relationships and Cardinality(a) Unary relationships
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(b) Binary relationships
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(c) Ternary relationships
Note: a relationship can have attributes of its own
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Cardinality Constraints
Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.
Minimum Cardinality If zero, then optional If one or more, then mandatory
Maximum Cardinality The maximum number
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Figure 2.8 Cardinality Mandatory and Optional
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(a) Basic relationship with only maximum cardinalities showing
(b) Mandatory minimum cardinalities
Figure 2.9 Cardinality Constraints
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Employees and departments – entities can be related to one another in more than one way
Figure 2.10 Examples of multiple relationships
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Strong vs. Weak Entities, andIdentifying Relationships
Strong entities exist independently of other types of entities has its own unique identifier represented with single-line rectangle
Weak entity dependent on a strong entity…cannot exist on its
own Does not have a unique identifier represented with double-line rectangle
Identifying relationship links strong entities to weak entities represented with double line diamond
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Associative Entities
It’s an entity – it has attributes
AND it’s a relationship – it links entities together When should a relationship with attributes instead be an
associative entity? All relationships for the associative entity should be many The associative entity could have meaning independent of
the other entities The associative entity preferably has a unique identifier,
and should also have other attributes The associative may be participating in other relationships
other than the entities of the associated relationship Ternary relationships should be converted to associative
entities
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Figure 2.11 An associative entity
Associative entity involves a rectangle with a diamond inside.Note that the many-to-many cardinality symbols face toward the associative entity and not toward the other entities
(a) An associative entity (CERTIFICATE)
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(b)Ternary relationship as an associative entity
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Components of E-R Model
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Recalled : Teaching Plan W2
Database design stages Conceptual data model Unified Modeling Language Entity Relationship Diagram (ERD)