Data management

Data management comprises all the disciplines related to managing data as a valuable resource. The official definition provided by DAMA is that "Data Resource Management is the development and execution of architectures, policies, practices and procedures that properly manage the full data lifecycle needs of an enterprise." This definition is fairly broad and encompasses a number of professions which may not have direct technical contact with lower-level aspects of data management, such as relational database management.

Data model
The term data model actually refers to two very different things: a description of data structure and the way data are organized using, for example, a database management system.

Data structure
A data model describes the structure of the data within a given domain and, by implication, the underlying structure of that domain itself. A data model may thus represent classes of entities about which a company wishes to hold information, the attributes of that information, and relationships among those entities. The model describes the organization irrespective of how data might be represented in a computer system.

The entities represented by a data model can be the tangible entities, but models that include such concrete entity classes tend to change over time. Robust data models often identify abstractions of such entities. For example, a data model might include an entity class called "Person", representing all the people who interact with an organization. Such an abstract entity class is typically more appropriate than ones called "Vendor" or "Employee", which identify specific roles played by those people.

A proper conceptual data model describes an organization's semantics. It is a collection of assertions about the nature of the organization. Proper entity classes are named with natural language words instead of technical jargon. Likewise, properly named relationships form concrete assertions about the organization. For example, an relationship called "is composed of" operating on entity classes "Order" and "Line item" forms the concrete assertion "Each Order is composed of one or more Line items."

Data organization
Another kind of data model describes how to organize data using a database management system or other data management technology. It describes, for example, relational tables and columns or object-oriented classes and attributes. Such a data model is sometimes referred to as the physical data model, but in the original ANSI three schema architecture, it is called "logical". In that architecture, the physical model describes the storage media (cylinders, tracks, and tablespaces). Ideally, this model is derived from the more conceptual data model described above. It may differ, however, to account for constraints like processing capacity and usage patterns.

While data analysis is a common term for data modeling, the activity actually has more in common with the ideas and methods of synthesis (inferring general concepts from particular instances) than it does with analysis (identifying component concepts from more general ones). {Presumably we call ourselves systems analysts because no one can say systems synthesists.} Data modeling strives to bring the data structures of interest together into a cohesive, inseparable, whole by eliminating unnecessary data redundancies and by relating data structures with relationships.