SQL Queries Questions and Answers by michael belete on Scribd
Posts
What is Data Flow Diagram (DFD)
Data Flow Diagram Symbols. DFD Library Data Flow Diagram Symbols. DFD Library Data Flow Diagrams graphically represent the information transfers and process steps of a system. They visually depict how data are processed by a system in terms of inputs and outputs, how occurs the input in a system, how the data flow through an information system and where they are stored, and how occurs output from the system. DFDs give the overview of the system and models the processes aspects, they are maintained with other methods of structured systems analysis. The main goal of DFDs is achievement of understanding between developers and users. For their construction are used two notations - Gane-Sarson and Yourdon, each of them uses its own set of symbols. Data Flow Diagrams solution from Software Development area extends the ConceptDraw PRO software with templates, samples, and predesigned libraries of data flow diagram symbols for both notations, allowing you...
Entity Relationship Diagram
entity-relationship diagram (model) By Vangie Beal An entity relationship model, also called an entity-relationship (ER) diagram, is a graphical representation of entities and their relationships to each other, typically used in computing in regard to the organization of data within databases or information systems. An entity is a piece of data-an object or concept about which data is stored. Relationships Between Entities A relationship is how the data is shared between entities. There are three types of relationships between entities: 1. One-to-One One instance of an entity (A) is associated with one other instance of another entity (B). For example, in a database of employees, each employee name (A) is associated with only one social security number (B). 2. One-to-Many One instance of an entity (A) is associated with zero, one or many instances of another entity (B), but for one instance of entity B there is only on...
Data flow diagram Data flow diagram example. [1] A data flow diagram ( DFD ) is a graphical representation of the "flow" of data through an information system , modelling its process aspects. A DFD is often used as a preliminary step to create an overview of the system, which can later be elaborated. [2] DFDs can also be used for the visualization of data processing (structured design). A DFD shows what kind of information will be input to and output from the system, where the data will come from and go to, and where the data will be stored. It does not show information about the timing of process or information about whether processes will operate in sequence or in parallel (which is shown on a flowchart ). Contents 1 History 2 Theory 2.1 Physical DFD 3 See also 4 References 5 Further reading 6 External links History Larry Constantine , the original developer of structured design, [3] based on Martin and Estrin...