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

Data and Process Modeling n 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 n 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) n Documents firm’s data by identifying types of data entities and their interrelationships n Prepared at “big picture” point of data specification n Very flexible A-3

Entity Types n Environmental n Resource n Important transaction Entity symbol A-4

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

Connectivity Time card A. One to one Produces Payroll check B. One to many ContainsInvoice C. Many to many Customer PurchasesProduct 11 1M M M Inventory item Number of times an entity occurs in relation to another entity A-6

Attributes n Characteristics of an entity n Actually data elements n Identifiers are unique attributes of the entity n 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

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

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

Fills Purchase order Supplier Represents Accounts payable Contains Raw Material Supplier number Supplier name Supplier address 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 Supplier number Supplier name Supplier address Total accounts payable Item number Item description Warehouse location Item unit price Balance on hand Reorder point Order quantity Quantity on hand 1 M M 1 MM Data Elements are Mapped A-11

PURCHASE ORDER NUMBER Purchase order date Supplier number Supplier Supplier address Purchase order amount PURCHASE ORDER PURCHASE ORDER LINE RAW MATERIAL CONTAINS REPRESENTS PURCHASE ORDER NUMBER LINE/ITEM NUMBER ITEM NUMBER Item number Item description Item quantity ordered Item unit price Item extended price Item description Warehouse location Item unit price Balance on hand Recorder point Order quantity Quantity on order 1M11 Normalized Portion of ERD A-12

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

Data Dictionary [cont.] n Data store dictionary entry describes unique data stored in a DFD n Data structure dictionary entry is completed for each structure listed on the data store and data flow forms n 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

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 Data Structure Dictionary Entry 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: Typical value: Specific values: Other editing details: A-18

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