103016352010

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Data DictionaryWhat does “Backordered item” mean?

What does “New Customer info.” contain?

How does the “account receivable report” look like?

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Data Dictionary

• A list of names used in the system modelsarranged alphabetically and their meaningand information about them

• Types of information provided: – Description of data

– If composite data, describe elements

– Data representation or type – Creator, creation date, user contacts

– Other names for the data (aliases)

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Data Dictionary

• Data dictionary is a metadata

• Created in parallel with DFD

• Created in top-down approach

• Data dictionary should be kept up-to-datewith the DFD model

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Data Dictionary

• Advantages: – Documentation for the whole system

– Eliminate redundancy in a system which has been

created by different people – Identify aliases

– Provide a starting point to develop reports andscreens

– Validates the data flow diagrams for completenessand accuracy

– Develop the logic for DFD processes

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Data Dictionary Contents

Data dictionaries contain:

– Data flow.

– Data structures.

– Elements.

– Data stores.

– Process

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Data flow Description

• ID number

• Name (as it appears in DFD)

• Description

• Source• Destination

• Type (file, screen, report, form, internal)

• Data structure name• How frequently produced

• Comments

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Defining Data Flow (Continued)

– The source of the data flow

• This could be an external entity, a process, or adata flow coming from a data store.

– The destination of the data flow – Type of data flow, either:

• A record entering or leaving a file.

• Containing a report, form, or screen.

• Internal - used between processes.

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Data Store

• ID number• Name• Alias name

• Description• Type (manual, computerized)• File format (database, sequential, Indexed)• Maximum/ average number of recording

– This helps the analyst to predict the amount of diskspace required.

• File name• Data structure

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Data Structure

• For compositional data flow and data storeelements

• Describe the elements of the data structureusing algebraic notation

= Composed of

{ } Repetition

( ) Optional+ and

[ / ] or

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Data Structure

• Example:Student record= student ID +

Student name+

Address +Date of birth +

Gender +

Nationality +

Telephone number +

(mobile telephone number)+

{ course record}

Course record= course name +Course number+Grade

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Data Elements

• Each element in the data structure should bedescribed – ID number

– Name

– Alias

– Description

– Type (Base: entered from user, derived: computed)

– Length (in characters) [max or fixed]

– Data type (date, numeric, alphanumeric)

– Input/Output format

– Validation criteria

– Default value

– Comments

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Defining Elements

– Aliases, which are synonyms or other namesfor the element

– These are names used by different users within

different systems – Example, a Customer Number may be called a:

• Receivable Account Number.

• Client Number.

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Defining Elements

• A base element is one that has beeninitially keyed into the system.

– Input from an external entity in the DFD

• A derived element is one that is created bya process, usually as the result of acalculation or some logic.

– Output from a process in the DFD

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Data Store Definition

• If the file is computerized, the file formatdesignates whether the file is a database fileor the format of a traditional flat file.

• The maximum and average number ofrecords on the file

• The growth per year

– This helps the analyst to predict the amount ofdisk space required.

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Data Store Definition

• The data set name specifies the table orfile name, if known.

– In the initial design stages, this may be left

blank.

• The data structure should use a namefound in the data dictionary.

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Logical and Physical data

• Logical data structures is what the usersees

• Physical data structure is what thesoftware needs for processing

– (e.g. flags, key fields for search, ..)

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Using the Data Dictionary

Data dictionaries may be used to:

– Create reports, screens, and forms.

– Generate computer program source code.

– Analyze the system design for completion andto detect design flaws.

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Creating Reports, Screens,Forms

To create screens, reports, and forms:

– Use the element definitions to create fields.

– Arrange the fields in an aesthetically pleasing

screen, form, or report, using designguidelines and common sense.

– Repeating groups become columns.

– Structural records are grouped together onthe screen, report, or form.

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Data Dictionary Analysis

• The data dictionary may be used inconjunction with the data flow diagram toanalyze the design, detecting flaws and

areas that need clarification.

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Data Dictionary Analysis(Continued)

• Some considerations for analysis are:

– All base elements on an output data flow mustbe present on an input data flow to the

process producing the output. – Base elements are keyed and should never

be created by a process.

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Process Data• Process number

• Process name

• Description

• Input

• Output• Type (batch, online, manual)

• Prewritten code: ready made functional libraries

• Process logic (Business rules)

• Reference to description tables or structures

• Unresolved issues: (notes to check with users)

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Process Specifications

• Process specifications are created for primitiveprocesses on a data flow diagram.

• They are also called minispecs.

• Advantages – Understand how the process works and go back to

users if not clear

– Describe what should happen for designer and

programmer

– Validate the DFD

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Structured English

• based on structured logic and Simple Englishstatements

• Appropriate technique for analyzing the system

when structured decisions are not complex. – Express all logic in terms of sequential structures,decision structures, case structures, or iterations.

– Use and capitalize accepted keywords such as IF,THEN, ELSE, DO, and PERFORM.

– Indent blocks of statements to show their hierarchy. – Underline words that have been described in the data

dictionary

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Describing Processes

• Example: Bonus monthly payment (StructuredEnglish)

For each customer

Read Customer recordFor each item rented between 1/10 to 1/11

add total

End for

If total is greater than or equal to 50$ then

send bonus and thank you letter

End if

End for

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Automatic Data Dictionary

• Using CASE tools:

– Easy to change and add

– Created and integrated with other models

– Checks that the DFD is valid

• e.g. all data needed for a process is input to it

• Data store contains data input/ output to/from it

• Derived data should be output from process• Checks data source and destination in DFD

– Use data structures to create reports andscreens

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