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information modelling

Entity-Relationship Model

In software engineering, an entity-relationship model (ERM) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams, ER diagrams, or ERDs.

The definitive reference for entity-relationship modelling is Peter Chen's 1976 paper[1]. However, variants of the idea existed previously, and have been devised subsequently.[2]

[1] "The Entity Relationship Model: Toward a Unified View of Data".

[2] A.P.G. Brown, "Modelling a Real-World System and Designing a Schema to Represent It", in Douque and Nijssen (eds.), Data Base Description, North-Holland, 1975, ISBN 0-7204-2833-5

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The first stage of information system design uses these models during the requirements analysis to describe information needs or the type of information that is to be stored in a database. The data modeling technique can be used to describe any ontology (i.e. an overview and classifications of used terms and their relationships) for a certain area of interest. In the case of the design of an information system that is based on a database, the conceptual data model is, at a later stage (usually called logical design), mapped to a logical data model, such as the relational model; this in turn is mapped to a physical model during physical design. Note that sometimes, both of these phases are referred to as "physical design".

There are a number of conventions for entity-relationship diagrams (ERDs). The classical notation mainly relates to conceptual modeling. There are a range of notations employed in logical and physical database design, such as IDEF1X.

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An entity may be defined as a thing which is recognized as being capable of an independent existence and which can be uniquely identified. An entity is an abstraction from the complexities of some domain. When we speak of an entity we normally speak of some aspect of the real world which can be distinguished from other aspects of the real world.[3]
An entity may be a physical object such as a house or a car, an event such as a house sale or a car service, or a concept such as a customer transaction or order. Although the term entity is the one most commonly used, following Chen we should really distinguish between an entity and an entity-type. An entity-type is a category. An entity, strictly speaking, is an instance of a given entity-type. There are usually many instances of an entity-type. Because the term entity-type is somewhat cumbersome, most people tend to use the term entity as a synonym for this term.
Entities can be thought of as nouns. Examples: a computer, an employee, a song, a mathematical theorem. Entities are represented as rectangles.

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A relationship captures how two or more entities are related to one another. Relationships can be thought of as verbs, linking two or more nouns. Examples: an owns relationship between a company and a computer, a supervises relationship between an employee and a department, a performs relationship between an artist and a song, a proved relationship between a mathematician and a theorem. Relationships are represented as diamonds, connected by lines to each of the entities in the relationship.

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Entities and relationships can both have attributes. Examples: an employee entity might have a Social Security Number (SSN) attribute; the proved relationship may have a date attribute. Attributes are represented as ellipses connected to their owning entity sets by a line.

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Every entity (unless it is a weak entity) must have a minimal set of uniquely identifying attributes, which is called the entity's primary key.

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Entity-relationship diagrams don't show single entities or single instances of relations. Rather, they show entity sets and relationship sets. Example: a particular song is an entity. The collection of all songs in a database is an entity set. The eaten relationship between a child and her lunch is a single relationship. The set of all such child-lunch relationships in a database is a relationship set. In other words, a relationship set corresponds to a relation in mathematics, while a relationship corresponds to a member of the relation.

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Certain cardinality constraints on relationship sets may be indicated as well.

T.L. Ramey

Organisation(s)

IDEF1 was developed under ICAM program priority 1102 by Dr. Robert R. Brown of the Hughes Aircraft Company, under contract to SofTech, Inc. Dr. Brown had previously been responsible for the development of IMS while working at Rockwell International (Rockwell chose not to pursue IMS as a marketable product; International Business Machines (IBM), which had served as a support contractor during development, subsequently took over the product and was successful in further developing it for market.) Dr. Brown credits his Hughes colleague Mr. Timothy Ramey as the inventor of IDEF1 as a viable formalism for modeling information structures. The two Hughes researchers built on ideas from and interactions with many luminaries in the field at the time. In particular, IDEF1 draws on the following techniques:

- the Evolving Natural Language Information Model (ENALIM) technique of Dr. G. M. Nijssen (Control Data Corporation) — this technique is now more widely known as NIAM or the Object-Role Model ORM;

- the network data structures technique, popularly called the CODASYL approach, of Dr. Charles Bachman (Honeywell Information Systems);

- the hierarchical data management technique, implemented in IBM's IMS data management system, developed by Dr. R. R. Brown (Rockwell International);

- the relational approach to data of Dr. E. F. Codd (IBM);

- The Entity-Relationship Approach (E-R) of Dr. Peter Chen (UCLA).

The effort to develop IDEF1 resulted in both a new method for information modeling and an example of its use in the form of a "reference information model of manufacturing." This latter artifact was developed by D. S. Coleman of the D. Appleton & Company (DACOM) acting as a sub-contractor to Hughes and under the direction of Mr. Ramey. Personnel at DACOM became quite expert at IDEF1 modeling and subsequently produced a training course and accompanying materials for the IDEF1 modeling technique.

The initial approach to IDEF information modeling (IDEF1) was published by the ICAM program in 1981, based on current research and industry needs. The theoretical roots for this approach stemmed from the early work of Edgar F. Codd on relational theory and Peter Chen on the entity-relationship model. The initial IDEF1 technique was based on the work of Dr. R.R. Brown and Mr. T.L. Ramey of Hughes Aircraft and Mr. D.S. Coleman of D. Appleton & Company, with critical review and influence by Charles Bachman, Peter Chen, Dr. M.A. Melkanoff, and Dr. G.M. Nijssen.

Dr. R.R. Brown

Organisation(s)

IDEF1 was developed under ICAM program priority 1102 by Dr. Robert R. Brown of the Hughes Aircraft Company, under contract to SofTech, Inc. Dr. Brown had previously been responsible for the development of IMS while working at Rockwell International (Rockwell chose not to pursue IMS as a marketable product; International Business Machines (IBM), which had served as a support contractor during development, subsequently took over the product and was successful in further developing it for market.) Dr. Brown credits his Hughes colleague Mr. Timothy Ramey as the inventor of IDEF1 as a viable formalism for modeling information structures. The two Hughes researchers built on ideas from and interactions with many luminaries in the field at the time. In particular, IDEF1 draws on the following techniques:

- the Evolving Natural Language Information Model (ENALIM) technique of Dr. G. M. Nijssen (Control Data Corporation) — this technique is now more widely known as NIAM or the Object-Role Model ORM;

- the network data structures technique, popularly called the CODASYL approach, of Dr. Charles Bachman (Honeywell Information Systems);

- the hierarchical data management technique, implemented in IBM's IMS data management system, developed by Dr. R. R. Brown (Rockwell International);

- the relational approach to data of Dr. E. F. Codd (IBM);

- The Entity-Relationship Approach (E-R) of Dr. Peter Chen (UCLA).

Logical Database Design Technique (LDDT)

LDDT had been developed in 1982 by Robert G. Brown of The Database Design Group entirely outside the IDEF program and with no knowledge of IDEF1. Nevertheless, the central goal of IDEF1 and LDDT was the same: to produce a database neutral model of the persistent information needed by an enterprise by modeling the real-world entities involved. LDDT combined elements of the relational data model, the E-R model, and data generalization in a way specifically intended to support data modeling and the transformation of the data models into database designs.

LDDT included multiple levels of model, the modeling of generalization/specialization, and the explicit representation of relationships by primary and foreign keys, supported by a well defined role naming facility. The primary keys and unambiguously role-named foreign keys expressed sometimes subtle uniqueness and referential integrity constraints that needed to be known and honored by whatever type of database was ultimately designed. Whether the database design used the integrity constraint based keys of the LDDT model as database access keys or indexes was an entirely separate decision. The precision and completeness of the LDDT models was an important factor in enabling the relatively smooth transformation of the models into database designs. Early LDDT models were transformed into database designs for IBM's hierarchical database, IMS. Later models were transformed into database designs for Cullinet's network database, IDMS, and many varieties of relational database.

The graphic syntax of LDDT differed from that of IDEF1 and, more importantly, LDDT contained interrelated modeling concepts not present in IDEF1. Therefore, instead of extending IDEF1, Mary E. Loomis of DACOM wrote a concise summary of the syntax and semantics of a substantial subset of LDDT, using terminology compatible with IDEF1 wherever possible. DACOM labeled the result IDEF1X and supplied it to the ICAM program, which published it in 1985. (IEEE 1998, p. iii) (Bruce 1992, p. xii)

To satisfy the data modeling enhancement requirements that were identified in the IISS-6202 project, a sub-contractor, DACOM, obtained a license to the Logical Database Design Technique (LDDT) and its supporting software (ADAM).

IDEF1X Information Modeling

IDEFIX (Integration Definition for Information Modeling) is a data modeling language for the developing of semantic data models. IDEF1X is used to produce a graphical information model which represents the structure and semantics of information within an environment or system.

Use of the IDEF1X permits the construction of semantic data models which may serve to support the management of data as a resource, the integration of information systems, and the building of computer databases. This standard is part of the IDEF family of modeling languages in the field of software engineering.

In 1983, the U.S. Air Force initiated the Integrated Information Support System (I2S2) project under the ICAM program. The objective of this project was to provide the enabling technology to logically and physically integrate a network of heterogeneous computer hardware and software. As a result of this project, and industry experience, the need for an enhanced technique for information modeling was recognized.

From the point of view of the contract administrators of the Air Force IDEF program, IDEF1X was a result of the ICAM IISS-6201 project and was further extended by the IISS-6202 project. To satisfy the data modeling enhancement requirements that were identified in the IISS-6202 project, a sub-contractor, DACOM, obtained a license to the Logical Database Design Technique (LDDT) and its supporting software (ADAM). From the point of view of the technical content of the modeling technique, IDEF1X is a renaming of LDDT.

LDDT had been developed in 1982 by Robert G. Brown of The Database Design Group entirely outside the IDEF program and with no knowledge of IDEF1. Nevertheless, the central goal of IDEF1 and LDDT was the same: to produce a database neutral model of the persistent information needed by an enterprise by modeling the real-world entities involved. LDDT combined elements of the relational data model, the E-R model, and data generalization in a way specifically intended to support data modeling and the transformation of the data models into database designs

The graphic syntax of LDDT differed from that of IDEF1 and, more importantly, LDDT contained interrelated modeling concepts not present in IDEF1. Therefore, instead of extending IDEF1, Mary E. Loomis of DACOM wrote a concise summary of the syntax and semantics of a substantial subset of LDDT, using terminology compatible with IDEF1 wherever possible. DACOM labeled the result IDEF1X and supplied it to the ICAM program, which published it in 1985.

IDEF1 Information Modeling

Body

From Wikipedia: IDEF1:

'The ICAM Program [..] developed a series of techniques known as the IDEF (ICAM Definition) Methods which included the following [..] IDEF1 used to produce an “information model” which represents the structure and semantics of information within the environment or system.'

IDEF1 was developed under ICAM program priority 1102 by Dr. Robert R. Brown of the Hughes Aircraft Company, under contract to SofTech, Inc. Dr. Brown had previously been responsible for the development of IMS while working at Rockwell International (Rockwell chose not to pursue IMS as a marketable product; International Business Machines (IBM), which had served as a support contractor during development, subsequently took over the product and was successful in further developing it for market.) Dr. Brown credits his Hughes colleague Mr. Timothy Ramey as the inventor of IDEF1 as a viable formalism for modeling information structures. The two Hughes researchers built on ideas from and interactions with many luminaries in the field at the time. In particular, IDEF1 draws on the following techniques:

- the Evolving Natural Language Information Model (ENALIM) technique of Dr. G. M. Nijssen (Control Data Corporation) — this technique is now more widely known as NIAM or the Object-Role Model ORM;

- the network data structures technique, popularly called the CODASYL approach, of Dr. Charles Bachman (Honeywell Information Systems);

- the hierarchical data management technique, implemented in IBM's IMS data management system, developed by Dr. R. R. Brown (Rockwell International);

- the relational approach to data of Dr. E. F. Codd (IBM);

- The Entity-Relationship Approach (E-R) of Dr. Peter Chen (UCLA).

LDDT had been developed in 1982 by [node:1684] of The Database Design Group entirely outside the IDEF program and with no knowledge of IDEF1. LDDT combined elements of the relational data model, the E-R model, and generalization in a way specifically intended to support data modeling and the transformation of the data models into database designs. The graphic syntax of LDDT differed from that of IDEF1 and, more importantly, LDDT contained interrelated modeling concepts not present in IDEF1. Mary E. Loomis wrote a concise summary of the syntax and semantics of a substantial subset of LDDT, using terminology compatible with IDEF1 wherever possible. DACOM labeled the result IDEF1X and supplied it to the ICAM program.

The effort to develop IDEF1 resulted in both a new method for information modeling and an example of its use in the form of a "reference information model of manufacturing." This latter artifact was developed by D. S. Coleman of the D. Appleton & Company (DACOM) acting as a sub-contractor to Hughes and under the direction of Mr. Ramey. Personnel at DACOM became quite expert at IDEF1 modeling and subsequently produced a training course and accompanying materials for the IDEF1 modeling technique.

The initial approach to IDEF information modeling (IDEF1) was published by the ICAM program in 1981, based on current research and industry needs. The theoretical roots for this approach stemmed from the early work of Edgar F. Codd on relational theory and Peter Chen on the entity-relationship model. The initial IDEF1 technique was based on the work of Dr. R.R. Brown and Mr. T.L. Ramey of Hughes Aircraft and Mr. D.S. Coleman of D. Appleton & Company, with critical review and influence by Charles Bachman, Peter Chen, Dr. M.A. Melkanoff, and Dr. G.M. Nijssen.