l545 systems analysis & design week 10: november 4, 2008

L545 Systems Analysis & Design

Week 10: November 4, 2008

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Data Dictionary

A data dictionary subsystem keeps track of: the definitions of all the data items in the

database Relationships that exist between various

data structures Screen and report format definitions that

may be used by various application programs

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Data Dictionaries: Purpose

To provide unambiguous definitions of all system data

Communicate/validate definitions to all participants in the analysis process: Analyst Users System designers

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Level of Data Dictionary

Data Elements Data Structure Data flows and Data Stores

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Data Elements Data elements are pieces of data, which

need not be broken further. Data elements can describe files, data

flows, or processes. Often a data element is self-defining,

e.g., Student name, enrolment no.

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Data Structure Data structure is defined as collection of

data elements

For example, let us consider the following "Student Information Record"

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Level of Data Dictionary Data Structure

E.g., "Student Information Record“ Student Information

Enrolment Number Student name

First name Last name Middle name

STUDENT INFORMATION" is a data structure, made up of data elements: student name and enrolment number

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Data flow and data stores Data flows are paths along which data

travels Data stores are places where data is

stored until needed Data flows are Data structures in motion Data stores are Data structures at rest

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Sample Entry: Attribute

A library reserves processing system

ITEM

Item_status

Item_title

Item_id

Item_author

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A library reserves processing system

ITEM

Item_title

Item_id

Item_authorItem_status

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A library reserves processing systemItem Status

Alias: Book status, Article statusMeaning: The current status of the reserve item

being processedData type: 1 characterPossible values:

L = lostT = tracedR = recalled from current borrowerW = in library workroomS = on reserve shelf (processing complete)

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Name is entry name (e.g., item status) Alias = a synonym for a previously-defined

data item Meaning = the semantic aspect of the

attribute (i.e., definition) Data type:

at least length and encoding means Specify the possible values

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Examples of Data Formats in PC Systems (Kendall & Kendall, p. 254

Data Type MeaningChar, text Any alphanumeric character

Datetime Alphanumeric data, several formats

Decimal, numeric Numeric data that are accurate to the least significant digit

Currency Monetary numbers accurate to four decimal places

Autonumber A number that is always incremented by one when a record is added to a database table

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Sample entry: Complex attribute

Catalog ordering system

Customer addressAlias: Client addressMeaning: the full mailing address of

the person ordering the materials; the address to which the materials are to be delivered

Composition: Street address + (Apt. number) + City + State + Zip

codeNote: No P.O. numbers allowed;

U.S. addresses only

optional

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Sample entry: Complex attribute

Define the composition of the entry Partition/decompose the data into its

components Components = the data elements which

make up the complex attribute

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Notation for Composition

+ and; includes all the components listed

[ ] or; select one of the alternatives given

separate components with | { } repetition of the component

enclosed, 0-n ( ) enclosed component is optional

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Implementing a Data Dictionary

Accompanies E-R diagram Provide additional detail about entities and

attributes Also provide:

Meanings of entities/relationships Notes on entities/relationship

Ordering of entities By entity/relationship Alphabetical, within entity/relationship

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Implementing a Data Dictionary

Minimize redundancy to ease maintenance Do not represent anything that is

represented elsewhere Use simple conventions for writing

definitions

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What Does DD Look Like?

First, compile a list of fields that appear on existing forms and reports (see Davis p. 76-77)

For typical data dictionary entries, see Davis p. 84

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Example

STUDENT

PID

Name Phone

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Example: Data dictionarySTUDENT: An individual person who takes a seminar and work PID Meaning: An identification number assigned to uniquely identify each student Data type: numeric/symbolic Possible values: 00000-99999Name Meaning: The name of the student Data type: alphanumeric, up to 30 characters including punctuationPhone Composition: area code + number

Phone area codeMeaning: area code of the student phone numberData type: alphanumeric, 3 characters

Phone numberMeaning: local number of the student phone number Data type: alphanumeric, 7 characters

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Mapping Specialization & Generalization Relationships

ACADEMIC PERSON

STUDENT FACULTY

d

PID

Major Appointment

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Mapping Specialization & Generalization Relationships

ACADEMIC_PERSON

PID Name Address

STUDENT

PID Major

FACULTY

PID Appointment

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Example: Data dictionaryACADEMIC_PERSON: An individual person who belongs to a

university PID Meaning: An identification number assigned to uniquely identify

each academic person Data type: numeric/symbolic Possible values: 00000-99999

STUDENT: An individual academic person who is taking coursesPID

Inherited from ACADEMIC_PERSON.PIDMajor Meaning: The major that the student is pursuing Data type: alphanumeric, up to 30 characters including punctuation

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Example: Data dictionaryFACULTY: An individual academic person who is teaching coursesPID

Inherited from ACADEMIC_PERSON.PIDAppointment Meaning: The school of college that the faculty member has an

appointment Data type: 4 characters Possible values:

ANTH = Anthropology BIOL = Biology HIST = History JOUR = Journalism PHYS = Physics …… SLIS = School of Library & Information Science

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Example

ATTEND

Passed?

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Example: Data dictionary

ATTEND: the seminar attended by studentsPassed Meaning: whether the student attended the session Data type: 1 character Possible values:

Y = Yes N = No

l545 systems analysis & design week 10: november 4, 2008

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