A data structure diagram (DSD) is the visual representation of a certain kind of

data model A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to the properties of real-world entities. For instance, a data model may specify that the data element representing a car be ...

that contains entities, their relationships, and the constraints that are placed on them. It is an older alternative to the

entity–relationship model An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can e ...

. The basic graphic notation elements of DSDs are

box A box (plural: boxes) is a container with rigid sides used for the storage or transportation of its contents. Most boxes have flat, parallel, rectangular sides (typically rectangular prisms). Boxes can be very small (like a matchbox) or v ...

es which represent entities. Arrow symbols represent relationships. Data structure diagrams are most useful for documenting complex data entities.

Overview

A data structure diagram is a

diagram A diagram is a symbolic Depiction, representation of information using Visualization (graphics), visualization techniques. Diagrams have been used since prehistoric times on Cave painting, walls of caves, but became more prevalent during the Age o ...

type that is used to depict the structure of

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

elements in the

data dictionary A data dictionary, or metadata repository, as defined in the ''IBM Dictionary of Computing'', is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format". ''Oracle Corporation, ...

. The data structure diagram is a graphical alternative to the

composition Composition or Compositions may refer to: Arts and literature *Composition (dance), practice and teaching of choreography * Composition (language), in literature and rhetoric, producing a work in spoken tradition and written discourse, to include ...

specifications within such data dictionary entries. The data structure diagrams is a predecessor of the

(E–R model). In DSDs, attributes are specified inside the entity boxes rather than outside of them, while relationships are drawn as boxes composed of attributes which specify the constraints that bind entities together. DSDs differ from the E–R model in that the E–R model focuses on the relationships between different entities, whereas DSDs focus on the relationships of the elements within an entity. There are several styles for representing data structure diagrams, with the notable difference in the manner of defining

cardinality The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thum ...

. The choices are between arrow heads, inverted arrow heads ( crow's feet), or numerical representation of the cardinality.

Bachman diagram

A Bachman diagram is a certain type of data structure diagram,IRS Resources
Part 2. Information Technology, Chapter 5. Systems Development, Section 13. Database Design Techniques and Deliverables. Retrieved 2 July 2009. and is used to design the

with a network or relational "logical" model, separating the

from the way the data is stored in the system. The model is named after database pioneer

Charles Bachman Charles William Bachman III (December 11, 1924 – July 13, 2017) was an American computer scientist, who spent his entire career as an industrial researcher, developer, and manager rather than in academia. He was particularly known for his ...

, and mostly used in computer

software design Software design is the process of conceptualizing how a software system will work before it is implemented or modified. Software design also refers to the direct result of the design process the concepts of how the software will work which co ...

. In a relational model, a relation is the cohesion of attributes that are fully and not of every key in that relation. The coupling between the relations is based on accordant attributes. For every relation, a rectangle has to be drawn and every coupling is illustrated by a line that connects the relations. On the edge of each line, arrows indicate the cardinality: 1-to-''n'', 1-to-1 and ''n''-to-''n''. The latter has to be avoided and must be replaced by 2 (or more) 1-to-''n'' couplings.

Overview

Bachman diagram

See also

References

Further reading