Tài chính kế toán - Documentation techniques and databases

Documentation techniques and databasesLearning objectives To learn about data flow diagrams (DFDs) and the symbols used in them.To understand a context diagram and its decomposition.To understand the standard symbols used in flow charts. To describe and construct different types of flow charts.To understand the advantages of flow charts over written descriptions.To be able to compare and contrast DFDs and flow charts.To understand decision tables and their relevance to programming.To learn about the construction of E-R diagrams as a basis for databases.key termsattributebinary notationbitbytecontext diagramdata dictionarydata flowdata flow diagramdata model data storedata structuredata warehousedatabasedatabase management systemdecision tabledecomposition of a data flow diagramkey terms (cont.)documentationentityE-R diagramflow chartsflow lineforeign keylead timeprimary keyrelational database modelrelationshipschemasecondary keysubschemaData flow diagramsGraphically describe the flow of data within an organisationComposed of four basic elements represented by standard symbols:Basic data flow diagramData flow diagram for customer delivery datesContext diagramsShow major data flows into and out of a systemDescribe each subsystem as a process showing interrelationship of those subsystems and their relationship to main systemContext diagramsDepict logical flow of data in summary formThe starting point for studying any systemDepict the system at its highest levelReferred to as level zero data flow diagramsFlow chartsDocument physical flows determined after logical data flows have been documented using data flow diagramsFlow chart symbolsAdvantages and disadvantages of flow chartsAdvantages:Enable any system to be represented in easily understandable mannerOverall picture of system easily seenHighlight relationship among different parts of the systemDisadvantages:Creation can be time-consumingNumerous symbols can be confusingProcess may not be completely representable using symbolsSystem flow chartsShow the relationship between input, processing and output including data, documents and storageRepresent the relationship between various processesSystem flow chartDocument flow chartsEmphasise the flow of documents between various people, groups and departments of an organisationProgram flow chartsShow the detailed steps of a computer programShow the logic and processing steps used to develop a computer programDecision tablesList the decision logic of a program flow chart in tabular formConstructed with two main columns and two rows:First row is further divided into a number of rows of conditionsSecond row is further divided into a number of rows of actionsDecision tablesThe decision table tells us the following:if stock is not available and floor stock is not being sold, collect 10% advanceif stock is available but delivery is not within three days, collect 10% advanceif stock is available and delivery within three days, collect full value of saleif stock is not available but floor stock is being sold within three days, collect full value of saleif stock is not available but floor stock is being sold after three days, collect 10% advanceDatabasesDatabase:the actual physical repository for an organisation’s dataDatabase management system (DBMS): a computer program that allows authorised users to update files, select and retrieve dataacts as an interface between database and application programsData structure:the technique of physically arranging records in a databaseDatabasesData warehouse:database constructed for ease of use and ad hoc queriesData dictionary:a document that describes each data element in the databaseTypes of database modelsDatabase management systems use different structures depending on the needs of the particular system:Hierarchical database modelNetwork database modelRelational database modelHierarchical database modelAlso called a tree model, occurs when data is organised in top-down structure in a one-to-many relationshipNetwork database modelAn extention of the hierarchical model but takes the form of a many-to-many relationshipRelational database modelLogical structure that views a database as a collection of two-dimensional tables called database tables