DATA AND PROCESS DATA AND PROCESS MODELINGMODELING

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Describe data and process modeling concepts and tools, including data flow diagrams, a data dictionary, and process descriptions

Describe the symbols used in data flow diagrams and explain the rules for their use

Draw data flow diagrams in a sequence, from general to specific

Explain how to level and balance a set of data flow diagrams

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Describe how a data dictionary is used and what it contains

Use process description tools, including structured English, decision tables, and decision trees

Describe the relationship between logical and physical models

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In chapter 3, you use data and process modeling techniques to develop a logical model of the proposed system and document the system requirements Logical model shows what the system must do Physical model describes how the system will

be constructed

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Systems analysts use many graphical techniques to describe an information system

One popular method is to draw a set of DFD A data flow diagram (DFD) uses various symbols

to show how the system transforms input data into useful information

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During system analysis phase, you learn how to create a visual model of the IS using set of DFD

A data flow diagram (DFD) shows how data moves through an information system but does not show program logic or processing steps

A set of DFDs provides a logical model that shows what the system does, not how it does it

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DFDs use four basic symbols that represent Processes data flows data stores entities

▪ DFD in this course use Gane and Sarson symbol set

▪ Another popular symbol set is the Yourdon symbol set

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Process symbol Receives input data and produces output that

has a different content, form, or both Process contain the business logic, also called

business rules that transform data and produce the results

Symbol is rectangle with round corner

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▪ Data flow is the path for data to move from one part of IS to another

▪ Represents one or more data items

▪ The symbol for a data flow is a line with a single or double arrowhead

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Represent data that the system stores The physical characteristics of a data store are

unimportant because you are concerned only with a logical model

Is a flat rectangle that is open on the right side and closed on the left side

The name of data store appear between the lines and identify the data it contain

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Symbol is a rectangle, which may be shaded to make it look three-dimensional

Name of the entity appears inside the symbol DFD entity also called Terminators because

they are data origins or final destination Source – entity that supplies data to the system Sink - entity that receive data from the system Entity name is form of a dept, outside

organization, other IS, or person

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Create a graphical model of the information system based on your fact-finding results

Performing three step process Step 1: Draw a context diagram Step 2: Draw a diagram 0 DFD Step 3: Draw the lower-level diagrams

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When u draw a context diagram and other DFDs, follow several guidelines:

1. Draw the context diagram so it fits on one page

2. Use the name of the information system as the process name in the context diagram

3. Use unique names within each set of symbols

4. Do not cross lines5. Provide a unique name and reference

number for each process6. Obtain user input and feedback

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Context diagram = is a top level view of an IS that shows the system’s boundary and scope

Start by placing a single process symbol in the center of page

Identify it as process 0 (zero) Then, place system entity around the perimeter Use data flows to connect the entity to central

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Diagram 0 - Zooms in on the context diagram and shows major processes, data flows, and data stores

Must retain all the connections that flow into and out of process 0

Each process has a reference number Diverging data flow – is a data flow in which the

same data travels to two or more different locations

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If same data flows in both directions, you can use a double-headed arrow

Diagram 0 represents exploded view of process 0, so it shows more detail than the context diagram

The higher-level diagram is called Parent diagram

The lower-level diagram is called Child diagram When u create a set of DFD, u break the

processing logic down into smaller units called Functional primitive

Functional primitive = a process consists of a single function that is not exploded further

Diagram 0 for the context diagram DFD for a grading system.

Diagram 0 DFD for the order system.

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To create lower-level diagram, you must use leveling and balancing techniques

Leveling Is a process of drawing a series of increasingly

detailed DFDs until all functional primitive are identify

Exploding, partitioning, or decomposing Example refer page 163

Balancing Maintain consistency among set of DFD by ensures

that the input and output data flows align properly For example refer page 164

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Diagram 1 DFD shows details of the FILL ORDER process in the

order system

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Show sample of context diagram The process 0 symbol has 2 input flow and 2 output flow Process 0 considered as a black box, with no internal

detail shown In next slide, process 0 (the parent DFD) is exploded into

the next level of detail Now 3 processes, 2 data stores, 4 internal data flows are

visible The both DFD are balanced because the 4 data flows

into and out of process 0 are maintained DFD also leveled because each internal process is

numbered to show that it is a child of the parent process

Example of a parent DFD diagram, showing process 0 as a black box

In the next level of detail, the process 0 black box reveal 3 processes, 2 data stores and 4 internal data flows, which shown in the dashed line

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A data dictionary, or data repository, is a central storehouse of information about the system’s data

An analyst uses the data dictionary to collect, document, and organize specific facts about the system

Also defines and describes all data elements and meaningful combinations of data elements

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A data element, also called a data item or field, is the smallest piece of data that has meaning

Data elements are combined into records, also called data structures

A record is a meaningful combination of related data elements that is included in a data flow or retained in a data store

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Documenting the Data Elements You must document every data element in the

data dictionary The objective is the same: to provide clear,

comprehensive information about the data and processes that make up the system

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The following attributes usually are recorded and described▪ Data element name or label, Alias, Type and

length, Default value, Acceptable values - Domain and validity rules

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The following attributes usually are recorded and described▪ Source – could be a specific form, dept or

outside organization▪ Security – identification individual or dept

who have access for each data element▪ Responsible user(s) – identification user

responsible for entering and changing value for data element▪ Description and comments – allow to enter

additional notes

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In addition to documenting each data element, u must document all data flows in data dictionary

The typical attributes are as follows▪ Data flow name or label – as appear in DFD▪ Description▪ Alternate name(s)▪ Origin▪ Destination▪ Record▪ Volume and frequency

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You must document every DFD data store in data dict

Typical characteristics of a data store are▪ Data store name or

label▪ Description▪ Alternate name(s)▪ Attributes▪ Volume and frequency

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You must document every process

Typical characteristics of a process Process name or label Description Process number Process description

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Typical characteristics of an entity include Entity name Description Alternate name(s) Input data flows Output data flows

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Typical characteristics of a record include▪ Record or data

structure name▪ Definition or

description▪ Alternate name(s)▪ Attributes

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Data dictionary serves as central storehouse of doc for an IS It is created when the system is developed and updated You can obtain many valuable reports from data dictnry

include: An alphabetized list of all data elements by name A report describing each data element and indicating the

user or department that is responsible for data entry, updating, or deletion

A report of all data flows and data stores that use a particular data element

Detailed reports showing all characteristics of data elements, records, data flows, processes, or any other selected item stored in the data dictionary

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A process description documents the details of a functional primitive, and represents a specific set of processing steps and business logic

Using set of process descr tools, u create a model that is accurate, complete, concise

Typical process description tools include Structured English Decision tables Decision trees

When you analyze a functional primitive, you break the processing steps down into smaller units in a process called modular design

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Is based on combinations of three logical structures, sometimes called control structures, which serve as building blocks for the process1. Sequence2. Selection3. Iteration - looping

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Is a subset of standard English that describe logical processes clearly and accurately

When use structured English, must conform to the following rules: Use only the three building blocks of sequence,

selection, and iteration Use indentation for readability Use a limited vocabulary, including standard

terms used in the data dictionary and specific words that describe the processing rules

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Structured English

statements

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Structured English might look familiar to programming students because it resembles pseudocode

Although the technique are similar, but the primary purposes is to describe the underlying business logic, while programmers who concerned with coding use pseudocode as a shorthand for the actual code

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Shows a logical structure, with all possible combinations of conditions and resulting actions

When documenting processes, it is important to consider every possible outcome to ensure that you have overlooked nothing

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Can have more than two possible outcomes (example below)

Often are the best way to describe a complex set of conditions.

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Is a graphical representation of the conditions, actions, and rules found in a decision table

Whether to use a decision table or tree often is a matter of personal preference

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While structured analysis tools are used to develop a logical model for a new information system, such tools also can be used to develop physical models of an information system

A physical model shows how the system’s requirements are implemented

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What is the relationship between logical and physical model?

Many systems analysts create a physical model of the current system and then develop a logical model of the current system before tackling a logical model of the new system

Performing that extra step allows them to understand the current system better

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Many analyst follow a four-model approach Which means they develop a physical model of

the current system, a logical model of the current system, a logical model of the new system, and a physical model of the new system

Benefits: it gives a clear picture of current system functions before make any modification or improvements

Disadvantage: of the four-model approach is the added time and cost

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During data and process modeling, a systems analyst develops graphical models to show how the system transforms data into useful information

The end product of data and process modeling is a logical model that will support business operations and meet user needs

Data and process modeling involves three main tools: data flow diagrams, a data dictionary, and process descriptions

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Data flow diagrams (DFDs) graphically show the movement and transformation of data in the information system

DFDs use four symbols A set of DFDs is like a pyramid with the context

diagram at the top The data dictionary is the central documentation

tool for structured analysis

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Each functional primitive process is documented using structured English, decision tables, and decision trees

Structured analysis tools can be used to develop a logical model during one systems analysis phase, and a physical model during the systems design phase

Chapter 3 Complete