Bài giảng Systems Analysis and Design - Chapter 8: Analyzing Systems Using Data Dictionaries

Analyzing Systems Using Data DictionariesSystems Analysis and Design, 7eKendall & Kendall8© 2008 Pearson Prentice HallLearning ObjectivesUnderstand analysts use of data dictionaries for analyzing data-oriented systemsCreate data dictionary entries for data processes, stores, flows, structures, and logical and physical elements of the systems being studied, based on DFDsUnderstand the concept of a repository for analysts’ project information and the role of CASE tools in creating themRecognize the functions of data dictionaries in helping users update and maintain information systems2CatalogingData flow diagrams can be used to catalogData processesFlowsStoresStructuresElementsCataloging takes place with the data dictionary3Major TopicsThe data dictionaryThe data repositoryDefining data flowDefining data structuresDefining data elementsDefining data storesUsing the data dictionaryXML4The Data DictionaryA reference work of data about data (metadata)Collects and coordinates data terms, and confirms what each term means to different people in the organization5Need for Understanding the Data DictionaryProvide documentationEliminate redundancyValidate the data flow diagramProvide a starting point for developing screens and reportsDetermine the contents of data stored in filesTo develop the logic for DFD processesCreate XML6The Data RepositoryA data repository is a large collection of project informationIt includes:Information about the data maintained by the systemProcedural logic and use casesScreen and report designData relationshipsProject requirements and final system deliverablesProject management information7Figure 8.1 How data dictionaries relate to data flow diagrams8Data Dictionary CategoriesData flowsData structuresElementsData stores9Defining the Data Flow ID - identification numberUnique descriptive nameA general description of the data flowThe source of the data flowThe destination of the data flowType of data flowThe name of the data structure describing the elementsThe volume per unit timeAn area for further comments and notations10Figure 8.3 An example of a data flow description from World’s Trend Catalog Division11Describing Data StructuresData structures are made up of smaller structures and elementsAn algebraic notation is used to describe data structures12Algebraic NotationEqual sign, meaning “is composed of”Plus sign, meaning "and”Braces {} meaning repetitive elementsBrackets [] for an either/or situationParentheses () for an optional element13Figure 8.4 Data structure example for adding a customer order at World’s Trend Catalog Division14Structural RecordsA structure may consist of elements or structural recordsThese are a group of elements, such as:Customer NameAddressTelephoneEach of these must be further defined until they are broken down into their component elements15Structural Records Used in Different SystemsStructural records and elements that are used within many different systems are given a non-system-specific name, such as street, city, and zipThe names do not reflect a functional areaThis allows the analyst to define them once and use in many different applications16Structural Record Example17Logical and Physical Data StructuresLogical Show what data the business needs for its day-to-day operationsPhysicalInclude additional elements necessary for implementing the system18Physical Data StructuresKey fields used to locate recordsCodes to identify record statusTransaction codes to identify different record typesRepeating group entriesLimits on items in a repeating groupPassword19Figure 8.6 An element description form example from World’s Trend Catalog Division20Data Element CharacteristicsElement ID The name of the elementAliasesA short description of the elementElement is base or derivedElement lengthType of dataInput and output formatsValidation criteriaDefault valueAn additional comment or remark area21Element IDOptional entryAllows the analyst to build automated data dictionary entries22The Name of the ElementShould be:DescriptiveUniqueBased on what the element is commonly called in most programs or by the major user of the element23AliasesSynonyms or other names for the elementNames used by different users in different systemsA CUSTOMER NUMBER may also be called a RECEIVABLE ACCOUNT NUMBER or a CLIENT NUMBER24Short Description of the ElementAn example might be:Uniquely identifies a customer who has made any business transactions within the last five years25Element Is Base or DerivedA base element is one that has been initially keyed into the systemA derived element is one that is created by a process, usually as the result of a calculation or a series of decision making statements26Element Length What should the element length beSome elements have standard lengths, state abbreviations, zip codes, or telephone numbersFor other elements, the length may vary and the analyst and user community must decide the final length27Element Length ConsiderationsNumeric amount lengths Name and address fieldsOther fields28Name and Address Length Percent of data that willElement Length fit (U.S.)Last Name 11 98First Name 18 95Company Name 20 95Street 18 90City 17 9929Data TruncationIf the element is too small, the data will be truncatedThe analyst must decide how this will affect the system outputsIf a last name is truncated, mail would usually still be deliveredA truncated email address or Web address is not usable30Type of DataAlphanumeric or text dataFormatsMainframe: packed, binary, displayMicrocomputer (PC) formatsPC formats, such as Currency, Number, or Scientific, depend on how the data will be used31Figure 8.7 Some examples of data formats used in PC systems32Figure 8.8 Format character codes33Validation CriteriaEnsure that accurate data are captured by the systemElements are either:Discrete, meaning they have fixed valuesContinuous, with a smooth range of values34Default ValueInclude any default value the element may haveThe default value is displayed on entry screensReduces the amount of keyingDefault values on GUI screensInitially display in drop-down listsAre selected when a group of radio buttons are used35Comment or Remarks AreaThis might be used to indicate the format of the date, special validation that is required, the check-digit method used, and so on36Data StoresData stores are created for each different data entity being storedWhen data flow base elements are grouped together to form a structural record, a data store is created for each unique structural recordBecause a given data flow may only show part of the collective data that a structural record contains, many different data flow structures may need to be examined to arrive at a complete data store description37Describing the Data StoreThe Data Store IDThe Data Store Name An Alias for the tableA short description of the data storeThe file typeFile format38Describing the Data Store (Continued)The maximum and average number of records on the file as well as the growth per yearThe file or data set name specifies the file name, if knownThe data structure should use a name found in the data dictionaryPrimary and secondary keysComments39Figure 8.9 An example of a data store form for World’s Trend Catalog Division40Creating the Data DictionaryData dictionary entries Created after the data flow diagram is completed orCreated as the data flow diagram is being developedCreated using a top-down approach41Figure 8.11 Two data flow diagrams and corresponding data dictionary entries for producing an employee paycheck42Analyzing Input and OutputA descriptive name for the input or outputThe user contact responsibleWhether the data is input or outputThe format of the data flowElements indicating the sequence of the data on a report or screenA list of elements43Figure 8.12 An example of an input/output analysis form for World’s Trend Catalog Division44Developing Data StoresRepresent data at restContain information of a permanent or semipermanent (temporary) natureWhen data stores are created for only one report or screen, we refer to them as “user views”45Using the Data DictionaryTo have maximum power, the data dictionary should be tied into a number of systems programsMay be used toCreate screens, reports, and formsGenerate computer language source codeAnalyze the system design, detecting flaws and areas that need clarification46Create Screens, Reports, and FormsUse the element definition and their lengthsArrange the elements in a pleasing and functional way using design guidelines and common senseRepeating groups become columnsStructural records are grouped together on the screen, report, or form47Analyze the System Design, Detecting Flaws and Areas that Need ClarificationAll base elements on an output data flow must be present on an input data flow to the process producing the outputA derived element should created by a process and should be output from at least one process into which it is not inputThe elements that are present in a data flow coming into or going out of a data store must be contained in the data store48Using Data Dictionaries to Create XMLXML is used to exchange data between businessesXML addresses the problem of sharing data when users have different computer systems and software or different database management systemsXML documents may be transformed into different output formatsXML is a way to define, sort, filter, and translate data into a universal data language that can be used by anyoneXML may be created from databases, a form, software programs, or keyed directly into a document, text editor, or XML entry program49Using Data Dictionaries to Create XML (Continued)The data dictionary is an ideal starting point for developing XML contentA standard definition of the data is created using a set of tags that are included before and after each data element or structureXML elements may also include attributesThe XML document tends to mirror the data dictionary structure50Figure 8.16 Using a data dictionary entry to develop XML content. The XML document mirrors the data dictionary structure51XML Document Type Definitions Used to determine if the XML document content is validDTDs may be created using the data dictionaryDTD may be used to validate the XML document52Figure 8.17 A document type definition for the customer XML document53XML SchemasA more precise way to define the content of an XML documentIncludes exact number of times an element may occurIncludes type of data within elements54SummaryThe data dictionaryA reference work containing data about dataInclude all data items from data flow diagramsRepositoryA larger collection of project informationDefining data structuresDefining elements55Summary (Continued)Defining data storesData dictionary entriesUsing the data dictionaryData dictionary analysisData dictionary to XML56