View source for Data modeling

{{Short description|Creating a model of the data in a system}}
[[File:4-3 Data Modelling Today.svg|420px|thumb|The data modeling process. The figure illustrates the way data models are developed and used today . A [[Conceptual schema|conceptual data model]] is developed based on the data [[Requirement|requirement]]s for the application that is being developed, perhaps in the context of an [[Activity diagram|activity model]]. The data model will normally consist of entity types, attributes, relationships, integrity rules, and the definitions of those objects. This is then used as the start point for interface or database design.<ref name="MW99"/>]]{{Software development process}}
'''Data modeling''' in [[Software engineering|software engineering]] is the process of creating a [[Data model|data model]] for an [[Information system|information system]] by applying certain formal techniques. It may be applied as part of broader [[Model-driven engineering]] (MDD) concept.

== Overview ==
Data modeling is a [[Software development process|process]]  used to define and analyze data [[Requirement|requirement]]s needed to support the [[Finance:Business process|business process]]es within the scope of corresponding information systems in organizations. Therefore, the process of data modeling involves professional data modelers working closely with business stakeholders, as well as potential users of the information system.

There are three different types of data models produced while progressing from requirements to the actual database to be used for the information system.<ref name = "RS001">Simison, Graeme. C. & Witt, Graham. C. (2005). ''Data Modeling Essentials''. 3rd Edition. Morgan Kaufmann Publishers. {{ISBN|0-12-644551-6}}</ref>  The data requirements are initially recorded as a [[Conceptual schema|conceptual data model]] which is essentially a set of technology independent specifications about the data and is used to discuss initial requirements with the business stakeholders. The conceptual model is then translated into a [[Logical data model|logical data model]], which documents structures of the data that can be implemented in databases. Implementation of one conceptual data model may require multiple logical data models. The last step in data modeling is transforming the logical data model to a [[Physical data model|physical data model]] that organizes the data into tables, and accounts for access, performance and storage details. Data modeling defines not just data elements, but also their structures and the relationships between them.<ref>[http://knowledge.fhwa.dot.gov/tam/aashto.nsf/All+Documents/4825476B2B5C687285256B1F00544258/$FILE/DIGloss.pdf Data Integration Glossary]  {{webarchive|url=https://web.archive.org/web/20090320001015/http://knowledge.fhwa.dot.gov/tam/aashto.nsf/All+Documents/4825476B2B5C687285256B1F00544258/%24FILE/DIGloss.pdf |date=March 20, 2009 }}, U.S. Department of Transportation, August 2001.</ref>

Data modeling techniques and methodologies are used to model data in a standard, consistent, predictable manner in order to manage it as a resource. The use of data modeling standards is strongly recommended for all projects requiring a standard means of defining and analyzing data within an organization, e.g., using data modeling:

* to assist business analysts, programmers, testers, manual writers, IT package selectors, engineers, managers, related organizations and clients to understand and use an agreed upon semi-formal model that encompasses the concepts of the organization and how they relate to one another
* to manage data as a resource
* to integrate information systems
* to design databases/[[Data warehouse|data warehouse]]s (aka data repositories)

Data modeling may be performed during various types of projects and in multiple phases of projects. Data models are progressive; there is no such thing as the final data model for a business or application. Instead a data model should be considered a living document that will change in response to a changing business. The data models should ideally be stored in a repository so that they can be retrieved, expanded, and edited over time. [[Biography:Jeffrey L. Whitten|Whitten]] et al. (2004) determined two types of data modeling:<ref name="WBD04"/> 
* Strategic data modeling: This is part of the creation of an information systems strategy, which defines an overall vision and architecture for information systems. Information technology engineering is a methodology that embraces this approach.
* Data modeling during systems analysis: In [[Systems analysis|systems analysis]] logical data models are created as part of the development of new databases.

Data modeling is also used as a technique for detailing business [[Requirement|requirement]]s for specific [[Database|database]]s. It is sometimes called ''database modeling'' because a [[Data model|data model]] is eventually implemented in a database.<ref name="WBD04">Whitten, Jeffrey L.; [[Biography:Lonnie D. Bentley|Lonnie D. Bentley]], [[Biography:Kevin C. Dittman|Kevin C. Dittman]]. (2005). ''Systems Analysis and Design Methods''. 6th edition. {{ISBN|0-256-19906-X}}.</ref>

== Topics ==

=== Data models ===
{{main|Data model}}
[[File:3-4 Data model roles.svg|thumb|320px|How data models deliver benefit.<ref name="MW99"/>]]
Data models provide a framework for [[Data|data]] to be used within [[Information system|information system]]s by providing specific definition and format. If a data model is used consistently across systems then compatibility of data can be achieved. If the same data structures are used to store and access data then different applications can share data seamlessly. The results of this are indicated in the diagram. However, systems and interfaces are often expensive to build, operate, and maintain. They may also constrain the business rather than support it. This may occur when the quality of the data models implemented in systems and interfaces is poor.<ref name="MW99">Matthew West and Julian Fowler (1999). [https://sites.google.com/site/drmatthewwest/publications/princ03.pdf Developing High Quality Data Models] {{Webarchive|url=https://web.archive.org/web/20200909121755/https://d2024367-a-62cb3a1a-s-sites.googlegroups.com/site/drmatthewwest/publications/princ03.pdf?attachauth=ANoY7crjITgBSUdEyb3UlEOS2OxXk3r-iJk0-S4EfbK3PtqCZvEgcZwvpBiF3VGC7M0IMhTWLZoERz8Otd2Tu5Bquzo4NmuOxyeAzvQa0DZlSIea0KlbnoKFHPK9zM3Pg1p7f2b_OcaIv3_J8mkFK8rMoR_UABqsAM_Pa9wd6qHK1by_hBvYNRPKQZpTM4-rqh1D4x68mcRDzADCED8sFixAn4Nezq0zd_hunEOcJ8m7FSTyRa2xnOA%3D&attredirects=0 |date=September 9, 2020 }}. The European Process Industries STEP Technical Liaison Executive (EPISTLE).</ref>

Some common problems found in data models are:
* Business rules, specific to how things are done in a particular place, are often fixed in the structure of a data model. This means that small changes in the way business is conducted lead to large changes in computer systems and interfaces. So, business rules need to be implemented in a flexible way that does not result in complicated dependencies, rather the data model should be flexible enough so that changes in the business can be implemented within the data model in a relatively quick and efficient way.
* Entity types are often not identified, or are identified incorrectly.  This can lead to replication of data, data structure and functionality, together with the attendant costs of that duplication in development and maintenance. Therefore, data definitions should be made as explicit and easy to understand as possible to minimize misinterpretation and duplication.
* Data models for different systems are arbitrarily different. The result of this is that complex interfaces are required between systems that share data. These interfaces can account for between 25 and 70% of the cost of current systems. Required interfaces should be considered inherently while designing a data model, as a data model on its own would not be usable without interfaces within different systems.
* Data cannot be shared electronically with customers and suppliers, because the structure and meaning of data has not been standardised. To obtain optimal value from an implemented data model, it is very important to define standards that will ensure that data models will both meet business needs and be consistent.<ref name="MW99"/>

=== Conceptual, logical and physical schemas ===
[[File:4-2 ANSI-SPARC three level architecture.svg|thumb|320px|The ANSI/SPARC three level architecture. This shows that a data model can be an external model (or view), a conceptual model, or a physical model. This is not the only way to look at data models, but it is a useful way, particularly when comparing models.<ref name="MW99"/>]]

In 1975 ANSI described three kinds of data-model ''instance'':<ref>American National Standards Institute. 1975. ''ANSI/X3/SPARC Study Group on Data Base Management Systems; Interim Report''. FDT (Bulletin of ACM SIGMOD) 7:2.</ref>

* [[Conceptual schema]]: describes the semantics of a domain (the scope of the model). For example, it may be a model of the interest area of an organization or of an industry. This consists of entity classes, representing kinds of things of significance in the domain, and relationships assertions about associations between pairs of entity classes. A conceptual schema specifies the kinds of facts or propositions that can be expressed using the model. In that sense, it defines the allowed expressions in an artificial "language" with a scope that is limited by the scope of the model. Simply described, a conceptual schema is the first step in organizing the data requirements.
* [[Logical schema]]: describes the structure of some domain of information.  This consists of descriptions of (for example) tables, columns, object-oriented classes, and XML tags. The logical schema and conceptual schema are sometimes implemented as one and the same.<ref name="RS001"/>
* [[Physical schema]]: describes the physical means used to store data.  This is concerned with partitions, CPUs, [[Software:Tablespace|tablespace]]s, and the like.

According to ANSI, this approach allows the three perspectives to be relatively independent of each other. Storage technology can change without affecting either the logical or the conceptual schema. The table/column structure can change without (necessarily) affecting the conceptual schema.  In each case, of course, the structures must remain consistent across all schemas of the same data model.

=== Data modeling process ===
{{further|Database design}}
[[File:Data modeling context.svg|thumb|360px|Data modeling in the context of business process integration.<ref name="SS93">Paul R. Smith & Richard Sarfaty (1993). [http://www.osti.gov/energycitations/purl.cover.jsp;jsessionid=6192EDBFBAB7DCED13883C55F221221A?purl=/10160331-YhIRrY/ Creating a strategic plan for configuration management using Computer Aided Software Engineering (CASE) tools.] Paper For 1993 National DOE/Contractors and Facilities CAD/CAE User's Group.</ref>]]

In the context of [[Finance:Business process modeling#Business process integration|business process integration]] (see figure), data modeling complements [[Finance:Business process modeling|business process modeling]], and ultimately results in database generation.<ref name="SS93"/>

The process of designing a database involves producing the previously described three types of schemas - conceptual, logical, and physical. The database design documented in these schemas are converted through a Data Definition Language, which can then be used to generate a database.  A fully attributed data model contains detailed attributes (descriptions) for every entity within it. The term "database design" can describe many different parts of the design of an overall database system. Principally, and most correctly, it can be thought of as the logical design of the base data structures used to store the data. In the [[Relational model|relational model]] these are the [[Software:Table (database)|tables]] and views. In an [[Object database|object database]] the entities and relationships map directly to object classes and named relationships. However, the term "database design" could also be used to apply to the overall process of designing, not just the base data structures, but also the forms and queries used as part of the overall database application within the Database Management System or DBMS.

In the process, system interfaces account for 25% to 70% of the development and support costs of current systems. The primary reason for this cost is that these systems do not share a [[Common data model|common data model]]. If data models are developed on a system by system basis, then not only is the same analysis repeated in overlapping areas, but further analysis must be performed to create the interfaces between them. Most systems within an organization contain the same basic data, redeveloped for a specific purpose. Therefore, an efficiently designed basic data model can minimize rework with minimal modifications for the purposes of different systems within the organization<ref name="MW99"/>

=== Modeling methodologies ===

Data models represent information areas of interest. While there are many ways to create data models, according to Len Silverston (1997)<ref name="SIG97">Len Silverston, W.H.Inmon, Kent Graziano (2007). ''The Data Model Resource Book''. Wiley, 1997. {{ISBN|0-471-15364-8}}. Reviewed by [http://www.tdan.com/view-book-reviews/5593 Van Scott on tdan.com]. Accessed November 1, 2008.</ref> only two modeling methodologies stand out, top-down and bottom-up:  
* Bottom-up models or View Integration models are often the result of a reengineering effort. They usually start with existing data structures forms, fields on application screens, or reports. These models are usually physical, application-specific, and incomplete from an [[Enterprise architecture|enterprise perspective]]. They may not promote data sharing, especially if they are built without reference to other parts of the organization.<ref name="SIG97"/>
* Top-down [[Logical data model|logical data model]]s, on the other hand, are created in an abstract way by getting information from people who know the subject area. A system may not implement all the entities in a logical model, but the model serves as a reference point or template.<ref name="SIG97"/>
Sometimes models are created in a mixture of the two methods: by considering the data needs and structure of an application and by consistently referencing a subject-area model. In many environments the distinction between a logical data model and a physical data model is blurred. In addition, some [[Computer-aided software engineering|CASE]] tools don't make a distinction between logical and [[Physical data model|physical data model]]s.<ref name="SIG97"/>

=== Entity–relationship diagrams ===
{{main|Entity–relationship model}}
[[File:B 5 1 IDEF1X Diagram.jpg|thumb|550px|right|Example of an [[IDEF1X|IDEF1X]] entity–relationship diagrams used to model IDEF1X itself. The name of the view is mm. The domain hierarchy and constraints are also given. The constraints are expressed as sentences in the formal theory of the meta model.<ref name="FIPS184">[http://www.itl.nist.gov/fipspubs/idef1x.doc FIPS Publication 184] {{Webarchive|url=https://web.archive.org/web/20131203223034/http://www.itl.nist.gov/fipspubs/idef1x.doc |date=December 3, 2013 }} released of IDEF1X by the Computer Systems Laboratory of the National Institute of Standards and Technology (NIST). December 21, 1993.</ref>]]
There are several notations for data modeling. The actual model is frequently called "entity–relationship model", because it depicts data in terms of the entities and relationships described in the [[Data|data]].<ref name="WBD04"/> An entity–relationship model (ERM) is an abstract conceptual representation of structured data. Entity–relationship modeling is a relational schema [[Database model|database model]]ing method, used in [[Software engineering|software engineering]] to produce a type of [[Conceptual schema|conceptual data model]] (or [[Semantic data model|semantic data model]]) of a system, often a [[Relational database|relational database]], and its requirements in a [[Top-down and bottom-up design|top-down]] fashion.

These models are being used in the first stage of [[Information system|information system]] design during the [[Requirements analysis|requirements analysis]] to describe information needs or the type of [[Information|information]] that is to be stored in a [[Database|database]]. The [[Data model|data model]]ing technique can be used to describe any [[Ontology (computer science)|ontology]] (i.e. an overview and classifications of used terms and their relationships) for a certain [[Philosophy:Domain of discourse|universe of discourse]] i.e. area of interest.

Several techniques have been developed for the design of data models. While these methodologies guide data modelers in their work, two different people using the same methodology will often come up with very different results. Most notable are:

* [[Bachman diagram]]s
* [[Barker's notation]]
* [[Entity–relationship model|Chen's notation]]
* Data Vault Modeling
* [[Extended Backus–Naur form]]
* [[IDEF1X]]
* [[Object-relational mapping]]
* Object-Role Modeling and [[FCO-IM|Fully Communication Oriented Information Modeling]]
* Relational Model
* Relational Model/Tasmania

=== Generic data modeling ===
{{main|Generic data model}}
[[File:HL7 Reference Information Model.jpg|thumb|320px|Example of a Generic data model.<ref>Amnon Shabo (2006). [http://healthit.hhs.gov/portal/server.pt?open=512&objID=1263&mode=2 Clinical genomics data standards for pharmacogenetics and pharmacogenomics] {{Webarchive|url=https://web.archive.org/web/20090722232240/http://healthit.hhs.gov/portal/server.pt?open=512&objID=1263&mode=2 |date=July 22, 2009 }}.</ref>]]
Generic data models are generalizations of conventional [[Data model|data model]]s. They define standardized general relation types, together with the kinds of things that may be related by such a relation type. 
The definition of generic data model is similar to the definition of a natural language. For example, a generic data model may define relation types such as a 'classification relation', being a [[Binary relation|binary relation]] between an individual thing and a kind of thing (a class) and a 'part-whole relation', being a binary relation between two things, one with the role of part, the other with the role of whole, regardless the kind of things that are related.

Given an extensible list of classes, this allows the classification of any individual thing and to specify part-whole relations for any individual object. By standardization of an extensible list of relation types, a generic data model enables the expression of an unlimited number of kinds of facts and will approach the capabilities of natural languages. Conventional data models, on the other hand, have a fixed and limited domain scope, because the instantiation (usage) of such a model only allows expressions of kinds of facts that are predefined in the model.

=== Semantic data modeling ===
{{main|Semantic data model}}
The logical data structure of a DBMS, whether hierarchical, network, or relational, cannot totally satisfy the requirements for a conceptual definition of data because it is limited in scope and biased toward the implementation strategy employed by the DBMS. That is unless the semantic data model is implemented in the database on purpose, a choice which may slightly impact performance but generally vastly improves productivity.
[[File:A2 4 Semantic Data Models.jpg|thumb|320px|Semantic data models.<ref name="FIPS184"/>]]
Therefore, the need to define data from a conceptual view has led to the development of [[Semantic data model|semantic data model]]ing techniques. That is, techniques to define the meaning of data within the context of its interrelationships with other data. As illustrated in the figure the real world, in terms of resources, ideas, events, etc., are symbolically defined within physical data stores. A semantic data model is an [[Abstraction (computer science)|abstraction]] which defines how the stored symbols relate to the real world. Thus, the model must be a true representation of the real world.<ref name="FIPS184"/>

The purpose of semantic data modeling is to create a structural model of a piece of the real world, called "universe of discourse". For this, four fundamental structural relations are considered:
* Classification/instantiation: Objects with some structural similarity are described as instances of classes
* Aggregation/decomposition: Composed objects are obtained joining its parts
* Generalization/specialization: Distinct classes with some common properties are reconsidered in a more generic class with the common attributes

A semantic data model can be used to serve many purposes, such as:<ref name="FIPS184"/>
* Planning of data resources
* Building of shareable databases
* Evaluation of vendor software
* Integration of existing databases

The overall goal of semantic data models is to capture more meaning of data by integrating relational concepts with more powerful [[Abstraction (computer science)|abstraction]] concepts known from the [[Artificial intelligence|artificial intelligence]] field. The idea is to provide high level modeling primitives as integral part of a data model in order to facilitate the representation of real world situations.<ref>"Semantic data modeling" In: ''Metaclasses and Their Application''. Book Series Lecture Notes in Computer Science. Publisher Springer Berlin / Heidelberg. Volume Volume 943/1995.</ref>

== See also ==
* [[Architectural pattern]]
* [[Software:Comparison of data modeling tools|Comparison of data modeling tools]]
* [[Data (computer science)]]
* [[Data dictionary]]
* [[Document modelling|Document modeling]]
* [[Enterprise data modelling]]
* Entity Data Model
* [[Information management]]
* [[Information model]]
* [[Building information modeling]]
* [[Metadata modeling]]
* [[Three-schema approach]]
* Zachman Framework

== References ==
{{reflist|33em}}
* {{NIST-PD}}

== Further reading ==
* J.H. ter Bekke (1991). ''Semantic Data Modeling in Relational Environments''
* John Vincent Carlis, Joseph D. Maguire (2001). ''Mastering Data Modeling: A User-driven Approach''.
* Alan Chmura, J. Mark Heumann (2005). ''Logical Data Modeling: What it is and how to Do it''.
* Martin E. Modell (1992). ''Data Analysis, Data Modeling, and Classification''.
* M. Papazoglou, Stefano Spaccapietra, Zahir Tari (2000). ''Advances in Object-oriented Data Modeling''.
* G. Lawrence Sanders (1995). ''Data Modeling''
* Graeme C. Simsion, Graham C. Witt (2005). ''Data Modeling Essentials'''
* Matthew West (2011) ''Developing High Quality Data Models''

== External links ==
* [http://www.agiledata.org/essays/agileDataModeling.html Agile/Evolutionary Data Modeling]
* [http://www.softdevarticles.com/modules/weblinks/viewcat.php?cid=21 Data modeling articles] {{Webarchive|url=https://web.archive.org/web/20100307022237/http://www.softdevarticles.com/modules/weblinks/viewcat.php?cid=21 |date=March 7, 2010 }}
* [http://www.methodsandtools.com/archive/archive.php?id=9 Database Modelling in UML]
* [http://www.agiledata.org/essays/dataModeling101.html Data Modeling 101]
* [http://www.jhterbekke.net/SemanticDataModeling.html Semantic data modeling]
* [http://www.cems.uwe.ac.uk/~tdrewry/modeling.htm System Development, Methodologies and Modeling] Notes on by Tony Drewry
* [http://www.omg.org/cgi-bin/doc?ab/05-12-02 Request For Proposal - Information Management Metamodel (IMM)] of the Object Management Group
* [https://web.archive.org/web/20120625215800/http://www.ipl.com/papers/Data%20modelling%20is%20NOT%20JUST%20for%20DBMS%20part%201.pdf Data Modeling is NOT just for DBMS's Part 1] Chris Bradley
* [https://web.archive.org/web/20120626144315/http://www.ipl.com/papers/Data%20modelling%20is%20NOT%20JUST%20for%20DBMS%20part%202.pdf Data Modeling is NOT just for DBMS's Part 2] Chris Bradley

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