Data Flow Diagram

1. Zohaib Siddique presents Data Flow Diagram

2. What is it? A model that indicates the flow of data through a system. Represented using Data Flow Diagrams(DFD)

3. Data Flow Diagrams are: Used to perform structured analysis to determine logical requirements A graphical tool, useful for communicating with users, managers, and other IS personnel Useful for analyzing existing as well as proposed systems A relatively simple technique to learn and use

4. Purposes of DFDs Unexploded DFDs are useful to identify information requirements Exploded DFDs can be used for presentation education gathering feedback information from users

5. It is the first step towards implementation It helps guide the development of user interfaces Guides the user through choices and avoids meaningless steps Good way to verify requirements with your client. Advantages of DFD

6. Uses of DFDs Used to analyze the system to ensure that the design is complete Used to partition the system into programs Used for system documentation

7. Data Flows data in motion marks movement of data through the system - a pipeline to carry data connects the processes, external entities and data stores Unidirectional originate OR end at a process (or both) name as specifically as possible - reflect the composition of the data - a noun do not show control flow! Control flow is easy to identify- a signal with only one byte - (on/off). HINT: if you can't name it: either it's control flow, doesn't exist or you need to get more information!

8. Processes transform incoming data flows into outgoing data flows represent with a bubble or rounded square name with a strong VERB/OBJECT combination; examples: create_exception_report validate_input_characters calculate_discount process

9. Data Stores data at rest represents holding areas for collection of data, processes add or retrieve data from these stores name using a noun (do not use ‘file’) only processes are connected to data stores show net flow of data between data store and process. For instance, when access a DBMS, show only the result flow, not the request data store

10. Different Types of DFDs Context diagram Level-0 diagram (system diagram) Level-n diagram Primitive diagram

11. Context Diagram defines the scope of the system by identifying the system boundary contains: one process (which represents the entire system) all sources/sinks (external entities) data flows linking the process to the sources and sinks (external entities)

12. Level-0 Diagram describes the overall processing of the system show one process for each major processing step or functional requirement data flows from the context appear on system diagram also (level balancing) can show a single data store to represent all data in aggregate at this level can draw duplicate sources, sinks and data stores to increase legibility

13. Drawing a Level-0 Diagram list the major data stores list major business steps draw a segment for each business step assemble into single DFD re-organize until satisfied number processes

14. Functional Decomposition similar to a series of more detailed maps iterative process of breaking the description of a system into finer and finer detail to create a set of charts in which one process on a given chart is explained in greater detail on another chart referred to as exploding, partitioning, or leveling must use your judgment to decide what goes on each level show error and exception handling on lower levels (if at all)

15. Quality Guidelines Completeness all components included & in project dictionary Consistency between levels: balancing, leveling Timing considerations assume system never starts and never stops Iterative nature revisions are common Drawing primitives (lowest level) when to stop?

16. Users command & data Display info. Alarm type Sensor status Telephone no. tones Level 0 Control pannel display Control Pannel Safe Home Software Alarm Sensors Telephone line

17. Level 1 User commands & dataConfigure requestConfiguration information Stop StartConfig dataConfig . Information A/d msg passwordDisplay info. Valid ID msg Sensor info Alarm type Sensor status Telephone no.tones Control pannel Configure info Activate/Deactivate system Interact with user Display msg & status Control pannel display Process password Alarm Monitor system Sensors Telephone line

18. Level 2 Sensor information Alarm type Sensor information Alarm Data Sensor ID, type Telephone number Telephone number tones Sensor status Access against setup Generate alsrm signal Access aiainst setup Read sensors Dial Phone

19. And that’s the end.

20. INVITATION Yours existance will highly be appreciated on 16th August 2009 at 10:00PM in my wedding ceremony at Sheraton Hotel, Karachi. Invitation Cards will be handed to you soon.