信息时代的管理信息系统Module_C课件

1、Extended Learning Module CDesigning Databases and Entity-Relationship DiagrammingINTRODUCTIONDatabase collection of information that you organize and access according to the logical structure of that informationRelational database uses a series of logically related two-dimensional tables or files to

2、 store information in the form of a database DESIGNING & BUILDING A RELATIONAL DATABASEDefine entity classes & primary keysDefine relationships among classesDefine information for each relationRelation = table = fileUse a data definition language to create database Remember Solomon Enterprises?From

3、Chapter 3Provides concrete to commercial builders & home ownersChapter 3 the CRM side of Solomons databaseFocus now SCM side of Solomons database Remember Solomon Enterprises?Remember Solomon Enterprises?Solomons database tablesCustomerConcrete TypeOrderTruckEmployee Observations for Solomon5 concre

4、te typesHome foundation and walkwaysCommercial foundation and infrastructurePremier speckled (with gravel)Premier marblePremier shell Observations for SolomonObservations for Solomon6 raw materialsWaterCement pasteSandGravelMarbleShellMixing instructions are for a cubic yard Observations for Solomon

5、Some raw materials are in several concrete typesConcrete types require several raw materialsInventory (QOH) is tracked for all raw materials Observations for SolomonSuppliers provide raw materialsSolomon uses only 1 supplier for a given raw materialA supplier can provider several raw materials Obser

6、vations for SolomonWaterSupplier not trackedQOH not tracked Business Rules for SolomonGiven concrete type will have many raw materialsGiven raw material may appear in many concrete typesEach raw material has one and only one supplier Business Rules for SolomonA supplier may provide many raw material

7、sThere may be suppliers present not providing any raw materialsThese business rules are very important to remember STEP 1: DEFINE ENTITY CLASSES & PRIMARY KEYSEntity class concept typically, person, place, or thing about which you wish to store information and that you can identify with a unique key

8、 (primary key)Concrete TypeRaw MaterialSupplier STEP 1: DEFINE ENTITY CLASSES & PRIMARY KEYSPrimary key a field (or group of fields) that uniquely describe each recordA record in a database is sometimes called an instance (of an entity class) STEP 1: DEFINE ENTITY CLASSES & PRIMARY KEYSIn general, s

9、tay away from names for primary keys (duplicates)Concrete Type Concrete TypeRaw Material Raw Material IDSupplier Supplier ID STEP 1: DEFINE ENTITY CLASSES & PRIMARY KEYSSTEP 2: DEFINE RELATIONSHIPS AMONG ENTITY CLASSESTo define relationships, you create an E-R diagramEntity-relationship (E-R) diagra

10、m a graphic method of representing entity classes and their relationships E-R DiagramsUse 5 symbolsRectangle entity classDotted line relationship| - single relationship0 zero/optional relationshipCrows foot () multiple relationship E-R DiagramsE-R DiagramsFigure C.2 on page 375 reads asA Concrete Ty

11、pe is composed of Raw MaterialA Raw Material is used to create a Concrete TypeA Supplier provides a Raw MaterialA Raw Material is provided by a Supplier E-R Diagrams - CardinalityE-R diagrams show relationshipsThey also show numerical nature of relationshipsThis is called cardinality| - single relat

12、ionship0 zero/optional relationship - multiple relationship E-R Diagrams - CardinalityFollowing lines marked A:A Supplier may not provide any Raw Material (0) but may provide more than one Raw Material ()E-R Diagrams - CardinalityFollowing lines marked B:A Raw Material must be provided by a Supplier

13、 (|) and can only be provided by one Supplier (|) NormalizationNormalization process of assuring that a relational database structure can be implemented as a series of two-dimensional tablesWe will follow three rules of normalization Normalization RulesEliminate repeating groups or many-to-many rela

14、tionshipsAssure that each field in a relation depends only on the primary key for that relationRemove all derived fields from the relations Eliminating Many-to-Many RelationshipsA many-to-many relationship exists if there is a crows foot () on each endYou must eliminate these by creating an intersec

15、tion relation Eliminating Many-to-Many RelationshipsEliminating Many-to-Many RelationshipsIntersection (composite) relation a relation you create to eliminate a many-to-many relationshipIntersection relation will have a composite primary keyComposite primary key consists of the primary key fields fr

16、om the two intersecting relations Solomons New Database Structure Steps to Eliminate a Many-to-Many Relationship Draw the part of the E-R diagram with many-to-many relationshipWrite some primary keys for each relationCreate new E-R diagram with intersection relation in the middleWrite some composite

17、 primary keys for intersection relation Steps to Eliminate a Many-to-Many Relationship Create a meaningful name for intersection relationMove minimum cardinality next to left relation to the right of intersection relationMove minimum cardinality next to right relation to the left of intersection rel

18、ation Steps to Eliminate a Many-to-Many Relationship Maximum cardinality on both sides of intersection relation is always many ()General rule new minimum and maximum cardinalities for the 2 original relations will be one (|) and one (|) STEP 3: DEFINING INFORMATION FOR EACH RELATIONTo ensure that ea

19、ch field is in the right relation, ask the following question:“Does this piece of information depend only on the primary key for this relation?”Yes its in the correct relationNo Its in the wrong relation STEP 3: DEFINING INFORMATION FOR EACH RELATIONSee Figure C.6 on page 381Look at Raw Material rel

20、ationEvery field must depend only on Raw Material IDRaw Material Name, QOH, and Supplier ID doSupplier Name does not STEP 3: DEFINING INFORMATION FOR EACH RELATIONWhat does Supplier Name depend on?It depends on Supplier IDSupplier ID is primary key for Supplier relationTherefore, Supplier Name belongs only in Supplier relation STEP 3: DEFINING INFORMATION FOR EACH RELATIONSee Figure C.6 on page 381Do you see any derived information?Counts?Sums?Averages?If you see them, remove them STEP 3: DEFINING INFORMATION FOR EACH RELATIONRaw Material Total i