Data flow diagrams are used to depict where data comes from, what operations process that data and how the results are being used.
Data flow diagrams displays the way data is converted and they are usually used in transaction-based systems to show the the range of physical, logical, or manual system.
A data flow diagram shows the flow of data and the changes between entities and processes. It also shows the temporary or permanent data stores and the output from one process might be used as an input into another process.
Data flow diagrams can be made up of numerous levels of context diagrams. The highest level of the data flow diagram is a context diagram which shows the full system. The data flow diagram depicts the system as a whole, that is a conversion engine with entities as the data input.
The next level of data flow diagram is the level 1 diagram. Level 1 diagram
shows the processes connected to the system with the various input data,
converted output data, and data stores.The first level data flow diagram might be made up of numerous other levels.
Level 1 diagrams can be used to show the divisions of tasks, the data flows and the data storage.
The logical data flow diagrams depicts the future state, which is the state after the conversion and the physical data flow diagrams replicate all of the data stores, printers, forms, devices, and other presentation of data.
There are some components of data flow diagrams, which are:
1. Externals (Entity, Source, Sink): An external (entity, source, sink) is a person, organization, automated system, with the ability to process data or receive data.
An external is an entity which is outside the system. They are the origin and terminus of data, each external must have at least one data flow going to or
coming from it. Externals are depicted by a noun inside a rectangle.
2. Data Store: A data store is an entity which is used to store and retrieve data. The data store should have data flowing to and from it. The data store is
depicted as either two parallel lines or as an open-ended rectangle with a
label.
3. Process: A process can be a manual or an automatic task executed which converts data from an output into an output. The process should have data flowing to and from it . A process should have both a verb and a noun and is depicted as a circle or rectangle with rounded corners.
4. Data Flow: A data flis is the flow of data between an external, a process, and a data store. The data flows binds the processes together and they represent the inputs and outputs of each process. Every process converts an input into an output. Data flows are depicted as a line with an arrow shown between processes and it is named using a noun.
Data flow diagrams has both strengths and limitations, which include:
Strengths
- It can be used as a way to learn about the data and processes.
- It is a good way of describing the range of the systems, interfaces, and user interfaces that are connected to it.
- It helps with spotting replicated data elements.
- It shows links to other systems.
- It helps in establishing the borderlines of a system.
- It could form a part of the system documentation.
- It helps in describing the logic behind the data flow in a system.
Limitations
- It might be too difficult to use data flow diagrams for large-scale systems.
- Data flow diagrams might be too difficult for the stakeholders to understand.
- It does not show the order of the activities.
- It does not depict the actors in the process.