LU 6 Data Dictionary PDF

TMF1913 SYSTEM ANALYSIS & DESIGN Learning Unit 6: Analyzing Systems Using Data Dictionaries Adapted or modified by the SA&D Team Semester 1, 2024- 2025 2 Learning Objectives Understand how analysts use data dictionaries for analyzing data- oriented systems. Understand the co...

TMF1913 SYSTEM ANALYSIS & DESIGN Learning Unit 6: Analyzing Systems Using Data Dictionaries Adapted or modified by the SA&D Team Semester 1, 2024- 2025 2 Learning Objectives Understand how analysts use data dictionaries for analyzing data- oriented systems. Understand the concept of a repository for analysts’ project information and the role of CASE tools in creating them. Create data dictionary entries for data processes, stores, flows, structures, and logical and physical elements of the systems being studied, based on DFDs. Recognize the functions of data dictionaries in helping users update and maintain information systems. 3 Cataloging Data flow diagrams (DFDs) can be used to catalog: Data processes Flows Stores Structures Elements Cataloging takes place with the data dictionary 4 Major Topics The data dictionary The data Write repository an agenda here. agenda here. Defining data flow rite an Defining Write data structures an agenda here.. Defining data elements Defining data stores Using Write an theagenda here. data dictionary 5 The Data Dictionary A reference work of data about data (metadata) Collects and coordinates data terms, and confirms what each term means to different people in the organization Need for understanding the data dictionary Provide documentation Eliminate redundancy Validate the data flow diagram for completeness and accuracy Provide a starting point for developing screens and reports Determine the contents of data stored in files To develop the logic for DFD processes Create XML 6 The Data Repository A data repository – it is a large collection of project information It includes: Information about the data maintained by the system Procedural logic and use cases Screen and report design Data relationships Project requirements and final system deliverables Project management information 7 Source of Information The data dictionary is created by examining and describing the contents of the data flows, data stores, and processes. The four steps (2) Catalogue (3) Describe (4) Break data to take in (1) Enter basic data data structures into compiling a data processes flows structures data elements dictionary. 8 How Data Dictionaries Relate to Data Flow Diagrams 9 Data Dictionary Categories The four data dictionary categories should be developed to promote understanding of the data of the system. 1 Data flows 2 Data structures 3 Elements 4 Data stores 10 10 Defining the Data Flow ID—identification number Unique descriptive name Data flow is a It is the first A general description of the data flow collection of component to data elements be defined The source of the data flow The destination of the data flow Type of data flow Elements – The name of the data structure used to Data describing the elements describe Structure - The volume per unit of time details of group of each data elements An area for further comments and flow notations 11 11 An Example of a Data Flow Description from World’s Trend Catalog Division Represents the screen used to add a new CUSTOMER ORDER and to update the customer and item files. 12 12 An Example of a Data Flow Description 13 13 Describing Data Structures Data structures are made up of smaller structures and elements An algebraic notation is used to describe data structures Algebraic Notation Equal sign = means “is composed of” Plus sign + means “and” Braces { } mean repetitive elements Brackets [ ] for an either/or situation Parentheses ( ) for an optional element 14 14 Data Structure Example for Adding a Customer Order at World’s Trend Catalog Division How are the symbols used? 15 15 16 16 Structural Records A structure may consist of elements or structural records. These are a group of elements , such as: Customer name - made up of First Name, Middle Name, Last Name Address Telephone Each of these must be further defined until they are broken down into their component elements Structural records and elements that are used within many different systems are given a non-system-specific name, such as street, city, and zip. The names do not reflect a functional area This allows the analyst to define them once and use in many different applications. For example, City may be a customer city, supplier city, or employee city. 17 17 Structural Record Example Customer name, address, and telephone are groups of elements or structural records. 18 18 Logical and Physical Data Structures Logical Physical Show what data the business Include additional elements needs for its day-to-day necessary for implementing the operations system E.g.: Name, Address, Orders It is important that the logical design accurately reflect the mental model of how the user views the system. The physical data structures are designed using the logical data structures as a basis. 19 19 Physical Data Structures Key fields used to locate an example is an item number records Codes to identify record such as whether an employee is active or status inactive Transaction codes to identify a credit file containing records for returned different record types items as well as records of payments contain a count of how many items are in Repeating group entries the group Limits on items in a - repeating group might be used by a customer accessing a Password secure website 20 20 Data Element Characteristics Element ID The name of the element (descriptive and unique) Aliases (synonyms or other names) A short description of the element Element is base or derived Element length Type of data (alphanumeric or text data) Input and output formats Validation criteria Default value An additional comment or remark area 21 21 22 22 Data Element Description Characteristics Element ID Optional entry Allows the analyst to build automated data dictionary entries The Name of the Should be: Element o Descriptive o Unique Based on what the element is commonly called in most programs or by the major user of the element Aliases Synonyms or other names for the element Names used by different users in different systems A CUSTOMER NUMBER may also be called a RECEIVABLE ACCOUNT NUMBER or a CLIENT NUMBER Short Description of An example might be: Uniquely identifies a customer who has the Element made any business transactions within the last five years 23 23 Data Element Description Characteristics Element is Base or A base element is one that has been initially keyed into the system Derived A derived element is one that is created by a process, usually as the result of a calculation or a series of decision-making statements Element Length What should the element length be? o Some elements have standard lengths, state abbreviations, zip codes, or telephone numbers. o For other elements, the length may vary and the analyst and user community must decide the final length. Element Length Considerations o Numeric amount lengths o Name and address fields o Other fields 24 24 Data Element Characteristics: Element Length- Name and Address Length Percent of data that will Element Length fit (United States) For example, a name field of 11 characters will Last Name 11 98 accommodate 98 percent First Name 18 95 of the last names in the Company Name 20 95 United States. Street 18 90 City 17 99 Data Truncation § If the element is too small, the data will be truncated § The analyst must decide how this will affect the system outputs § If a last name is truncated, mail would usually still be delivered § A truncated email address or web address is not usable 25 25 Data Element Characteristics: Type of Data Alphanumeric or text data Formats Mainframe: packed, binary, display Microcomputer (PC) formats PC formats, such as Currency, Number, or Scientific, depend on how the data will be used Some examples of data formats used in PC systems (shown in the table) 26 26 Data Element Characteristics: Input and Output Formats Input and output formats should be included, using special coding symbols to indicate how the data should be presented. Each symbol represents one character/digit. If the same character repeats several times, the character followed by a number in parentheses indicating how many times the character repeats is substituted for the group. E.g. XXXXXXXX would be represented as X(8). Format Character Codes 27 27 Data Element Description Characteristics Validation Criteria Ensure that accurate data are captured by the system Elements are either: o Discrete, meaning they have fixed values o Continuous, with a smooth range of values Default Value Include any default value the element may have The default value is displayed on entry screens Reduces the amount of keying Default values on GUI screens Initially display in drop-down lists Are selected when a group of radio buttons are used For check boxes, the default value (either “yes” or “no”) determines whether or not the check box will have an initial check in it Comment or Remarks This might be used to indicate the format of the date, special validation Area that is required, the check-digit method used, and so on 28 28 Describing the Data Store The Data Store ID often mandatory to prevent the analyst from storing redundant information The Data Store Name descriptive and unique An Alias for the table such as CLIENT MASTER for the CUSTOMER MASTER The file type computer or manual File format database table or flat file The maximum and average helps the analyst to predict the amount of disk space number of records on the file required for the application, necessary for hardware as well as the growth per year acquisition planning. 29 29 Describing the Data Store The file or data set name specifies In the initial stages this item may be left blank. the file name, if known The data structure should use a Provides a link to the elements for this data store. name found in the data dictionary Primary and secondary keys must be elements (or a combination of elements) found in the data structure. o primary key should be unique. o secondary key is used to control record sequencing on reports and to locate records directly. Comments are used for information that does not fit into any of the above categories; update or backup timing, security and so on. 30 30 31 31 Creating the Data Dictionary The use of algebraic notation and structural records Created after the data flow allows the analyst to Data diagram is completed or, develop the data dictionary Created as the data flow diagram entries is being developed dictionary and the data flow diagrams using a top-down approach. Created using a top-down approach 32 32 Two Data Flow Diagrams and Corresponding Data Dictionary Entries for Producing an Employee Paycheck It is important that the data flow names on the child data flow diagram are contained as elements or structural records in the data flow on the parent process. i.e. WAGE INFORMATION is a structural record contained in the EMPLOYEE RECORD. 33 33 Analyzing Input and Output An important step in creating the data dictionary is to identify and categorize system input and output data flow. A descriptive name for the input or output The user contact responsible Whether the data is input or output The format of the data flow Elements indicating the sequence of the data on a report or screen A list of elements—including their names, lengths, and whether they are base or derived, and their editing criteria. 34 34 An Example of an Input/Output Analysis Form for World’s Trend Catalog Division Once the form has been completed, each element should be analyzed to determine whether the element repeats, whether it is optional, or whether it is mutually exclusive of another element. 35 35 Developing Data Stores Represent data at rest Contain information of a permanent or semi permanent (temporary) nature When data stores are created for only one report or screen, we refer to them as “user views” Using the Data Dictionary § To have maximum power, the data dictionary should be tied into a number of systems programs § May be used to § Create screens, reports, and forms § Generate computer language source code § Analyze the system design, detecting flaws and areas that need clarification 36 36 Create Screens, Reports, and Forms The data dictionary may be used to create screens, reports, and forms. For example, examine the data structure for the World’s Trend ORDER PICKING SLIP in Figure 1. Because the necessary elements and their lengths have been defined, the process of creating physical documents consists of arranging the elements in a pleasing and functional way using design guidelines and common sense. Repeating groups become columns, and Figure: Data structural records are grouped together on the structure for an order picking screen, report, or form. slip at World’s Trend Catalog Division. 37 37 Create Screens, Reports, and Forms The report layout for the World’s Trend ORDER PICKING SLIP is shown in Figure 2. Notice that FIRST NAME and LAST NAME are grouped together in NAME, and that QUANTITY (PICKED and ORDERED), SECTION, SHELF NUMBER, ITEM NUMBER, ITEM DESCRIPTION, SIZE, and COLOR form a series of columns, because they are the repeating elements. Figure: Order picking slip created from the data dictionary 38 38 Analyze the System Design, Detecting Flaws and Areas that Need Clarification All base elements on A derived The elements that are an output data flow element present in a data flow coming into or going out of a data store must be present on an input data flow to the should be created by process producing the a process and output must be contained in the data store should be output from at least one process into which it is not input 39 39 Benefits of Data Dictionaries The data dictionary is the An up-to-date one common data dictionary If begun early, a Automated data source in the can serve as an data dictionary dictionaries can organization for excellent can save many serve as answering reference for hours of time in references for questions and maintenance the analysis and both people and settling disputes efforts on design phases. programs. about any unfamiliar aspect of data systems. definition. Summary The data dictionary A reference work containing data about data Includes all data items from data flow diagrams Repository A larger collection of project information. Defining data structures Defining elements Defining data stores Data dictionary entries Using the data dictionary Data dictionary analysis