Appendix A Data Modeling MANAGEMENT INFORMATION SYSTEMS 8/E Raymond McLeod, Jr. and George Schell Appendix A Data Modeling A-1 Copyright 2001 Prentice-Hall, Inc. 1

Data and Process Modeling During systems development both processes and data must be modeled Data modeling describes data used by system Process modeling describes processes carried out by system Level of detail Varies between highest summary and lowest detail Structured tools enable level of detail to be varied A-2

Entity-Relationship Diagram (ERD) Documents firm’s data by identifying types of data entities and their interrelationships Prepared at “big picture” point of data specification Very flexible A-3

Entity Types Environmental Resource Important transaction Entity symbol A-4

An association between two entity types Relationship An association between two entity types Relationship symbol Time card Employee Fills out A-5

Number of times an entity occurs in relation to another entity Connectivity Number of times an entity occurs in relation to another entity 1 1 Payroll check Time card Produces A. One to one 1 M Inventory item Invoice Contains B. One to many M M Customer Purchases Product C. Many to many A-6 3

Attributes Characteristics of an entity Actually data elements Identifiers are unique attributes of the entity Descriptors describe the entity A-7

Preparation of an Entity-Relationship Diagram 1. Identify the entities 2. Identify the relationships 3. Prepare a rough ERD 4. Map data elements to the entities 5. Perform a data analysis (through third normal form is common) 6. Prepare a modified ERD 7. Review the ERD with users and refine A-8

Rough ERD Supplier number 1 Fills M Purchase order number M M Raw Material Contains M Represents Item number 1 Accounts payable Supplier number A-9 4

Normalization First normal form (1NF) Second normal form (2NF) Eliminate repeating elements in an entity Second normal form (2NF) Ensure that descriptor attributes rely on the entire composite key for the assignment of values Third normal form (3NF) Ensure that an attribute value cannot be determined by values of other attributes A-10

Data Elements are Mapped Supplier number Supplier name Supplier address Supplier Data Elements are Mapped 1 Purchase order number Purchase order date Supplier number Supplier name Supplier address Item number (n times) Item description (n times) Item quantity (n times) Item unit price (n times) Item extended price (n time) Purchase order amount Fills M M M Purchase order Raw Material Contains M Item number Item description Warehouse location Item unit price Balance on hand Reorder point Order quantity Quantity on hand Represents Supplier number Supplier name Supplier address Total accounts payable 1 Accounts payable A-11 4

Normalized Portion of ERD PURCHASE ORDER 1 M PURCHASE ORDER LINE 1 1 RAW MATERIAL CONTAINS REPRESENTS PURCHASE ORDER NUMBER LINE/ITEM NUMBER PURCHASE ORDER NUMBER Purchase order date Supplier number Supplier Supplier address Purchase order amount ITEM NUMBER Item description Warehouse location Item unit price Balance on hand Recorder point Order quantity Quantity on order Item number Item description Item quantity ordered Item unit price Item extended price A-12 6

Data Dictionary Written description of the data contained in the database First ones maintained in hardcopy form Most are now maintained on a computer Data flow dictionary entry describes data flows on DFD A-13

Data Dictionary [cont.] Data store dictionary entry describes unique data stored in a DFD Data structure dictionary entry is completed for each structure listed on the data store and data flow forms Data element dictionary entry is used for each data element, or attribute included in all of the structures A-14

Data Flow Dictionary Entry Data flow name: Sales Order Description: The documents that are filled out by customers to identify the products, and the quantities of each, that they will wish to purchase. From: 1. Open mail To: 2. Enter sales order information Data structures: Sales order record Comments: A-15

Data Store Dictionary Entry Data store name: Sales order form Description: The history file of sales order forms, after the data has been entered into the sales commission system. Data structures: Sales order record Volume: Approximately 140 per day Activity: Access: Order department personnel Comments: A-16

Data Structure Dictionary Entry Structure name: Sales order record Description: The sales order form that the customer uses to order merchandise. Date elements: Customer.Number Customer.Order.Number Salesperson.Number Customer.Order.Date *Item.Number *Item.Description *Item.Quantity *Item.Unit.Price *Item.Extended.Price Comments: Elements marked with asterisks occur for each item record A-17

Data Element Dictionary Entry Data element name: Salesperson.Number Description: The number that identifies the salesperson Type: Numeric Length: 4 No. decimal pos. Aliases: Salesman number, Sales rep number Range of values: 0001-9999 Typical value: Specific values: Other editing details: A-18

Summary During early years of computing, emphasis was on the processes performed. Currently, emphasis is on data ERDs are a primary tool in data analysis Data dictionaries provide a means of documenting data A-19