PEMODELAN SISTEM Process Modeling Data Modeling

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

Process Modelling Copyright 2001 Prentice-Hall, Inc. 1

Data Flow Diagrams (DFDs) Graphic representation of a system that uses a small number of symbol shapes to illustrate how data flows through interconnected processes Most natural way to document processes Emphasis on processes rather than data B-4

DFD Symbols DFDs consist of four symbols 1) Environmental elements called terminators Person Organization Another system 2) Processes which transform inputs to outputs Labeled with verb and object Also labeled with system or computer program name B-5

DFD Symbols [cont.] DFD symbols [cont.] Data flows which consist of logically related data elements that travel from one point or process to another. In other words, data in motion. Structures Diverge Converge B-6

DFD Symbols [cont.] DFD symbols [cont.] Data stores which are data repositories. In other words, data at rest. B-7

A Data Flow Diagram (Figure 0 Diagram) of a Sales Commission System Mail A Data Flow Diagram (Figure 0 Diagram) of a Sales Commission System Customer 1. Open mail Sales orders Entered sales orders 2. Enter sales order data Sales order form file Entered sales order data 3. Sort sales order s Sorted sales records Sales commission report Sales manager 4. Compute sales commissions B-8 4

When Drawing a Context Diagram 1. Use only a single process symbol 2. Label the process symbol to represent the entire system 3. Do not number the single process symbol 4. Include all terminators for the system 5. Show all the data flows between the terminators and the system B-9

Sales Commission System A Context Diagram of a Sales Commission System Customer Mail Sales Commission System Sales commission report Sales Manager B-10

Figure n Diagrams Documents a single process of a DFD in a greater amount of detail n represents the number of the process on the next higher level that is being documented The term “leveled DFDs” describe the hierarchy of diagrams ranging from context to the lowest-level figure n diagram B-11

Figure 4 Diagram of a Sales Commission System Sorted sales records 3 4.1 Compute commission amounts Sales commission report 4.2 Accumulate totals Sales manager Commission amounts B-12

How Many Levels to Use? Restrict a single DFD to no more than six to eight processes Use another tool to document the lowest level of detail but use no more than a single page. B-13

Data Flow Diagramming Guidelines 1. Label each data flow with a unique name. 2. Keep data flow names constant between levels. 3. Show proper disposition of records deleted from a data store. 4. When documenting a computer program, do not include reads/writes. 5. Avoid read-only processes. 6. Write-only processes are permissible when time serves as the trigger. B-14

Structured English Narrative form of computer code documentation Based on Pseudocode Abbreviated, formalized pseudocode in a particular format that looks like computer code B-15

Structured English Guidelines 1) Use a verb when describing each processing strip. 2) Supplement verb with one or more objects when necessary. 3) Use only three constructs of programming. Sequence Selection Repetition B-16

Structured English Guidelines [cont.] 4) Use only data names defined in the data dictionary. 5) Use uppercase for all data names and computer syntax. 6) Indent to show a hierarchical structure. B-17

Structured English Guidelines [cont.] 7) When documentation is subdivided into modules, use the first line of each module for an identifying label and leave at least one blank line in-between. 8) Restrict each module to a single entry and exit point. B-18

Structure English Example START Initialize storage TOTAL.SALES, TOT.COM = 0 Process sales data DO WHILE (more records) PERFORM READ DATA PERFORM PROCESS DATA PERFORM PRINT DATA END DO B-19

Summary Process modeling is an important part of system design Various techniques exist for process modeling DFDs Structured English Manager can use Structured English and DFDs to communicate system requirements B-20

Data Modelling A-21 Copyright 2001 Prentice-Hall, Inc. 1

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-22

Entity Types Environmental Resource Important transaction Entity symbol A-23

An association between two entity types Relationship An association between two entity types Relationship symbol Time card Employee Fills out A-24

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 Mahasiswa Sebagai dosen wali Dosen B. One to many M M Mahasiswa Mengambil Matakuliah C. Many to many A-25 3

Attributes Characteristics of an entity Actually data elements Identifiers are unique attributes of the entity Descriptors describe the entity A-26

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-27

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-28 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-29

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-30 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-31 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-32

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-33

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-34

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-35

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-36

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-37

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-38