A logical data model or logical schema is a

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 ...

of a specific problem domain expressed independently of a particular database management product or storage technology (

physical data model A physical data model (or database design) is a representation of a data design as implemented, or intended to be implemented, in a database management system. In the lifecycle of a project it typically derives from a logical data model, thou ...

) but in terms of data structures such as relational tables and columns, object-oriented classes, or XML tags. This is as opposed to a

conceptual data model A conceptual schema is a high-level description of informational needs underlying the design of a database. It typically includes only the main concepts and the main relationships among them. Typically this is a first-cut model, with insufficient ...

, which describes the semantics of an organization without reference to technology.

Overview

Logical data models represent the abstract structure of a domain of information. They are often diagrammatic in nature and are most typically used in business processes that seek to capture things of importance to an organization and how they relate to one another. Once validated and approved, the logical data model can become the basis of a

and form the design of a database. Logical data models should be based on the structures identified in a preceding

, since this describes the semantics of the information context, which the logical model should also reflect. Even so, since the logical data model anticipates implementation on a specific computing system, the content of the logical data model is adjusted to achieve certain efficiencies. The term 'Logical Data Model' is sometimes used as a

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are al ...

of ' domain model' or as an alternative to the domain model. While the two concepts are closely related, and have overlapping goals, a domain model is more focused on capturing the concepts in the problem domain rather than the structure of the data associated with that domain.

History

When ANSI first laid out the idea of a ''logical schema'' in 1975,American National Standards Institute. 1975. “ANSI/X3/SPARC Study Group on Data Base Management Systems; Interim Report”. FDT(Bulletin of ACM SIGMOD) 7:2. the choices were ''hierarchical'' and ''network''. The

relational model The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of t ...

– where data is described in terms of tables and columns – had just been recognized as a data organization theory but no software existed to support that approach. Since that time, an

object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...

approach to data modelling – where data is described in terms of classes, attributes, and associations – has also been introduced.

Logical data model topics

Reasons for building a logical data structure

* Helps common understanding of business data elements and requirement * Provides foundation for designing a database * Facilitates avoidance of

data redundancy In computer main memory, auxiliary storage and computer buses, data redundancy is the existence of data that is additional to the actual data and permits correction of errors in stored or transmitted data. The additional data can simply be a comple ...

and thus prevent data and business transaction inconsistency * Facilitates data re-use and sharing * Decreases development and maintenance time and cost * Confirms a logical process model and helps impact analysis.

Conceptual, logical and physical data model

A logical data model is sometimes incorrectly called a physical data model, which is not what the ANSI people had in mind. The physical design of a database involves deep use of particular database management technology. For example, a table/column design could be implemented on a collection of computers, located in different parts of the world. That is the domain of the physical model. Conceptual, logical and physical data models are very different in their objectives, goals and content. Key differences noted below.

References

External links

Building a Logical Data Model
By George Tillmann, DBMS, June 1995. {{DEFAULTSORT:Logical Data Model Data modeling