A logical data model in systems engineering

Systems engineering

Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...

 is a representation of an organization's data, organized in terms of entities and relationships and is independent of any particular data management technology.

Overview

Logical data models represent the abstract structure of some 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 physical data model

Physical data model

A physical data model is a representation of a data design which takes into account the facilities and constraints of a given database management system. In the lifecycle of a project it is typically derived from a logical data model, though it may be reverse-engineered from a given database...

 and inform the design of a database.

Logical data models should be based on the structures identified in a preceding conceptual data model, 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

Synonym

Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...

 of 'Domain Model

Domain model

A domain model in problem solving and software engineering can be thought of as a conceptual model of a domain of interest which describes the various entities, their attributes, roles and relationships, plus the constraints that govern the integrity of the model elements comprising that problem...

' 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, the choices were hierarchical and network. The relational model

Relational model

The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F...

 – 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 analysis and design

Object-oriented analysis and design is a software engineering approach that models a system as a group of interacting objects. Each object represents some entity of interest in the system being modeled, and is characterised by its class, its state , and its behavior...

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

Reasons for building a logical data model

• Helps common understanding of business data elements and requirements
• Provides foundation for designing a database
• Facilitates avoidance of data redundancy
  Data redundancy
  Data redundancy occurs in database systems which have a field that is repeated in two or more tables. For instance, in case when customer data is duplicated and attached with each product bought then redundancy of data is a known source of inconsistency, since customer might appear with different...
  
   and thus prevent data & 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.

Modeling benefits

• Facilitates business process
  Business process
  A business process or business method is a collection of related, structured activities or tasks that produce a specific service or product for a particular customer or customers...
  
   improvement
• Focuses on requirement
  Requirement
  In engineering, a requirement is a singular documented physical and functional need that a particular product or service must be or perform. It is most commonly used in a formal sense in systems engineering, software engineering, or enterprise engineering...
  
  s independent of technology
• Facilitates data re-use and sharing
  Data sharing
  Data sharing is the practice of making data used for scholarly research available to other investigators. Replication has a long history in science...
  
  
• Increases return on investment
  Return on investment
  Return on investment is one way of considering profits in relation to capital invested. Return on assets , return on net assets , return on capital and return on invested capital are similar measures with variations on how “investment” is defined.Marketing not only influences net profits but also...
  
  
• Centralizes metadata
  Metadata
  The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
  
  
• Fosters seamless communication between application
  Application
  Application may refer to:* Application for employment* Application software* Function application in mathematics and computer science...
  
  s
• Focuses communication for data analysis
  Data analysis
  Analysis of data is a process of inspecting, cleaning, transforming, and modeling data with the goal of highlighting useful information, suggesting conclusions, and supporting decision making...
  
   and project team members
• Establishes a consistent naming scheme
  Naming scheme
  A naming scheme is a plan for naming objects. In computing, naming schemes are often used for objects connected into computer networks.-Naming schemes in computing:Large networks often use a systematic naming scheme, such as using a location A naming scheme is a plan for naming objects. In...
  
  

Logical & 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.

People often get confused with the fact that logical and physical data models are very different in their objectives, goals and content. Following are some key differences.

Logical Data Model	Physical Data Model
Includes entities (tables), attributes (columns/fields) and relationships (keys)	Includes tables, columns, keys, data types, validation rules, database triggers, stored procedures, domains, and access constraints
Uses business names for entities & attributes	Uses more defined and less generic specific names for tables and columns, such as abbreviated column names, limited by the database management system (DBMS) and any company defined standards
Is independent of technology (platform, DBMS)	Includes primary keys and indices for fast data access.
Is normalized to fourth normal form Fourth normal form Fourth normal form is a normal form used in database normalization. Introduced by Ronald Fagin in 1977, 4NF is the next level of normalization after Boyce–Codd normal form . Whereas the second, third, and Boyce–Codd normal forms are concerned with functional dependencies, 4NF is concerned with a... (4NF)	May be de-normalized to meet performance requirements based on the nature of the database. If the nature of the database is Online Transaction Processing(OLTP) or Operational Data Store (ODS) it is usually not de-normalized. De-normalization is common in Datawarehouses.

See also

• Core Architecture Data Model
  Core Architecture Data Model
  Core architecture data model in enterprise architecture is a logical data model of information used to describe and build architectures....
  
  
• Database design
  Database design
  Database design is the process of producing a detailed data model of a database. This logical data model contains all the needed logical and physical design choices and physical storage parameters needed to generate a design in a Data Definition Language, which can then be used to create a database...
  
  
• Entity-relationship model
  Entity-relationship model
  In software engineering, an entity-relationship model 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...
  
  
• Logical schema
  Logical schema
  A Logical Schema is a data model of a specific problem domain expressed in terms of a particular data management technology. Without being specific to a particular database management product, it is in terms of either relational tables and columns, object-oriented classes, or XML tags...
  
  
• Object role modeling
  Object role modeling
  Object Role Modeling is a method for conceptual modeling, and can be used as a tool for information and rules analysis, ontological analysis, and data modeling in the field of software engineering.- Overview :...
  
  

External links

• Building a Logical Data Model By George Tillmann, DBMS, June 1995.