Data Flow Diagrams (DFD) - Concepts, Symbols, and Development, Exams of Nursing

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SSA - Exam 2 questions well answered already passed Data Flow Diagrams(DFD) - correct answer ✔✔- graphical representation of data processes and flows throughout the organization - emphasizes logic of underlying system - based on general systems model *Input ---> Process ---> Output Why use DFD? - correct answer ✔✔- logical information flow of the system - determination of physical system construction requirements - simplicity of notation - establishment of manual and automated systems requirements Advantages of DFD - correct answer ✔✔- early understanding of system technical implications - establishment of inter-relatedness between business and systems - determine if data and processes have been defined properly - user involvement with system development DFD - Four Symbols - correct answer ✔✔Process: oval/rounded square Data store: skinny rectangle Source/sink: normal rectangle Data flow: arrow Process - correct answer ✔✔work/actions performed on data so that they are transformed, stored, or distributed Data Store - correct answer ✔✔data at rest, notebook, file folder, database Source/Sink - correct answer ✔✔origin and/or destination of the data ("external entity" or just "Entity") (NOT THE SAME AS ERD ENTITY) Data Flow - correct answer ✔✔data in motion DFD Formatting Symbols - correct answer ✔✔Entity (square)- external to boundaries of system (sources and destinations of data) Data Flow (arrow)- data movement (electronic exchange; paper documents) Process (rounded square)- transformation of data (from input to output) Data Store (skinny rectangle)- data depository for (electronic files; paper files (sometimes shown as an upside down triangle) External Entities - correct answer ✔✔- supply data to the system - receive data/information from the system - but not considered part of the system Entity -Purchase Order-> Enter orders Data Flows - correct answer ✔✔- represent data being moved to or from (an external entity, a process, a data source) - shown as a line with arrowheads - labeled with description of the type of data, document, or report Enter orders -Orderdata-> Open order file Processes - correct answer ✔✔- set of task performed on data to convert inputs to outputs - labeled as a verb/noun (e.g., ENTER ORDERS) - data flow out always labeled differently than data flow in Entity -Purchase order-> Enter orders -Order data-> Open order file Processes - 4 types - correct answer ✔✔- reorganize input(sort, reformat, filter/select) - all child diagrams are broken into primitive processes - decision has to be made when to stop decomposition When do you stop decomposing? (Primitive DFD) - correct answer ✔✔- when all children diagrams are primitive - often when each data store represents data about a single entity ( no more "data normalization") - or when user does not need to see more detail - when you have shown each business transaction, form, report, or online display as a single data flow - when there is a single process for each choice on all lowest-level menu options Rules & Guidelines for DFD - correct answer ✔✔- a data store must always be connected to a process - external entity must always be connected to a process - data may flow out of one process and into another Naming Rules for Data Flows - correct answer ✔✔- data flows must be named (use a noun...what data re being used by a process?) - output flow from a process (must have a different name than the input flow, output cannot be the same as the input) - data traveling together (should be shown and named as one data flow, example: order and payments flowing together should be labeled as "orders and payments") Data Stores' Rules & Guidelines - correct answer ✔✔- if not input data flowing to them, may not be properly represented (where did the data in the data store come from?) - should be uniquely numbered on the flow diagram - description of the data attributes should be contained in a similarly numbered table structure/data attribute dictionary (you can create the dictionary by putting out the ACCESS data structures for each table) Rules & Guidelines for Processes - correct answer ✔✔- must have at least one input and one output data flow (if no input, process is creating from "thin air", if no output, process is "black hole" or "data sink") - data should be sent only to processes that use them - should be uniquely named and numbered - description of the process should be in a similarly numbered and indexed "process dictionary" - "primitive process" performs one simple, well-defined task (no further decomposition is possible, can be turned into one line of code) Common Errors - correct answer ✔✔- omitting data flow - placing arrowhead in the wrong direction - directly connecting data stores & external entities - labeling incorrectly - including more than 9 processes - having unbalanced decomposition Common DFD Errors - correct answer ✔✔- dual/split data flows - entity to entity/data store communication - no data output - no data input - data to data communication Logical DFD - correct answer ✔✔- focus on how the business operates - processes that exist regardless of the type of system implemented Physical DFD - correct answer ✔✔- details physical system requirements - contains construction specifications (software, hardware, people) Logical to Physical DFD - correct answer ✔✔1. create a logical DFD of the current system 2. add all data and processes not in the current system which must be present in the new system 3. derive the physical data flow diagram for the new system 4. logical DFD of the current system will lead to appropriate logical DFD of the new system 5. physical DFD will follow naturally if the logical DFD is accurate Logical DFD - advantages - correct answer ✔✔- better understanding of business processes - better communication (within developer team, between developers and users) - flexibility and maintenance - elimination of redundancies Physical DFD - advantages - correct answer ✔✔- builds design on clear logical requirements - clarifies manual & automated processes - detailed process description - identifying temporary data stores - specifying name of files and printouts - adding controls Dataflow Spliting - correct answer ✔✔- when composite data flow at higher level is split - different parts go to different processes in the lower level DFD - DFD remains balanced because same data is involved, but split into two parts Balancing DFDs - correct answer ✔✔Q. A composite data flow on one level can be split into component data flows at the next level, but not new data can be added and all data in the composite must be accounted for in one or more subflows R. The inputs in a process must be sufficient to produce the outputs from the process. Thus, all outputs can be produced, and all data in inputs move somewhere S. At the lowest level of DFDs, new data flows may be added to represent data that are transmitted under exceptional conditions; these data flows typically represent error messages T. To avoid having data flow lines cross each other, you may repeat data stores or sources/sinks on a DFD. Use an additional symbol, like a double line on the middle vertical line of a data store symbol or a diagonal line in a corner of a sink/source square, to indicate a repeated symbol Partitioning Data Flow Diagrams - correct answer ✔✔*the process of separating activities into groups based on automation, manual, and user needs* - identify separate user groups - process timing Cardinality("Business Rules") - correct answer ✔✔*expresses the specific number of records in the related table that are associated with one record in the first table* - shows the minimum and maximum (range) - examples: (0,1) means zero or one, (1,1,) means one and only one, (1,M) means at least one, but maybe many, (0,M) means any number ACCESS Relationship Diagrams - correct answer ✔✔- access automatically draws internal ER diagram - each table shown as an entity box (table attributes automatically listed inside the box, key fields shown in boldface) - you draw connecting lines between related tables(entities; relationship triangles not required by access, draw lines is related keys are connected) - specify the connectivity of the relationship (either 1 or ∞ ("many")) Data dictionary - correct answer ✔✔- defines each data element (field) - documents the metadata (data about the data) - described data structures - makes system development easier - "the database designer's database" - part of the "data repository" Data Dictionary - Metadata - correct answer ✔✔- filed name (an aliases) - data type (alpha, numeric, data, logical) - field length (number of positions) - input mask, format, caption - description (source, verification, uses, etc.) - primary key? required? Data Repository (part of CASE Tools) - correct answer ✔✔- information about the data (data flows/data stores/structures, relationships between data elements - procedural logic - design of screens, forms, & reports - design project management information (schedules, requirements, users, etc.) MS Access Data Types - correct answer ✔✔- text - memo - number - date/time - currency - counter - yes/no - OLS Object MS Access Field Properties - correct answer ✔✔- filed name - description - data type - field size - caption - required? - default value - default places - input mask - indexed