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 c ...

that contains entities, their relationships, and the constraints that are placed on them. The basic graphic notation elements of DSDs are boxes which represent entities. The arrow symbol represents relationships. Data structure diagrams are most useful for documenting complex data entities.

Overview

Data Structure Diagram is a diagram type that is used to depict the structure of

data In the pursuit of knowledge, data (; ) is a collection of discrete Value_(semiotics), values that convey information, describing quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of sy ...

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'' defines it ...

. The data structure diagram is a graphical alternative to the composition specifications within such data dictionary entries. The data structure diagrams is a predecessor of 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 ex ...

(E–R model). In DSDs,

attribute Attribute may refer to: * Attribute (philosophy), an extrinsic property of an object * Attribute (research), a characteristic of an object * Grammatical modifier, in natural languages * Attribute (computing), a specification that defines a prope ...

s 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 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. 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. We have 1-to-''n'', 1-to-1 and ''n''-to-''n''. The latter has to be avoided and must be replaced by two (or more) 1-to-''n'' couplings.

Overview

Bachman diagram

See also

References

Further reading