In database modeling, a first class item is one that has an identity independent of any other item. The identity allows the item to persist when its attributes change, and allows other items to claim relationships with the item.
A database model is a type of data model that determines the logical structure of a database and fundamentally determines in which manner data can be stored, organized and manipulated. The most popular example of a database model is the relational model, which uses a table-based format.
An identity in object-oriented programming, object-oriented design and object-oriented analysis describes the property of objects that distinguishes them from other objects. This is closely related to the philosophical concept of identity.
As a general rule, first class items represent things rather than relationships. For example, the database representations of a human and of a company are each first class items. However, the fact that the person is an employee of that company is not a first class item. Likewise, data about that relationship, e.g. information about the salary the company pays to its employee, is not a first class item.
Typically, a relational database will include several tables, each of which contains rows representing first class items of a given type (e.g. a table of people, a table of companies). It will also contain other tables representing relationships between these first class items.
A relational database is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970. A software system used to maintain relational databases is a relational database management system (RDBMS). Virtually all relational database systems use SQL for querying and maintaining the database.
A table is an arrangement of data in rows and columns, or possibly in a more complex structure. Tables are widely used in communication, research, and data analysis. Tables appear in print media, handwritten notes, computer software, architectural ornamentation, traffic signs, and many other places. The precise conventions and terminology for describing tables vary depending on the context. Further, tables differ significantly in variety, structure, flexibility, notation, representation and use. In books and technical articles, tables are typically presented apart from the main text in numbered and captioned floating blocks.
In the context of a relational database, a row—also called a tuple—represents a single, implicitly structured data item in a table. In simple terms, a database table can be thought of as consisting of rows and columns. Each row in a table represents a set of related data, and every row in the table has the same structure.
In a table representing first class items, one column of the table will typically contain a different integer assigned to each row (effectively, to each item) as a unique identifier: that is to say, unique for objects of this type; objects of different types, represented in different tables, can coincidentally have the same identifier, but the coincidence is meaningless.
A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. The term column applies especially to a large round support with a capital and a base or pedestal which is made of stone, or appearing to be so. A small wooden or metal support is typically called a post, and supports with a rectangular or other non-round section are usually called piers. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces. Other compression members are often termed "columns" because of the similar stress conditions. Columns are frequently used to support beams or arches on which the upper parts of walls or ceilings rest. In architecture, "column" refers to such a structural element that also has certain proportional and decorative features. A column might also be a decorative element not needed for structural purposes; many columns are "engaged", that is to say form part of a wall.
An integer is a number that can be written without a fractional component. For example, 21, 4, 0, and −2048 are integers, while 9.75, 51/2, and √2 are not.
An identifier is a name that identifies either a unique object or a unique class of objects, where the "object" or class may be an idea, physical [countable] object, or physical [noncountable] substance. The abbreviation ID often refers to identity, identification, or an identifier. An identifier may be a word, number, letter, symbol, or any combination of those.
In a relational database, a table representing a relationship between two or more first class items (or data about that relationship) will usually not have special identifiers for its rows. Instead these rows will be identified by an ordered tuple consisting of unique identifiers of the first class items involved in the relationship.
In mathematics, a tuple is a finite ordered list (sequence) of elements. An n-tuple is a sequence of n elements, where n is a non-negative integer. There is only one 0-tuple, an empty sequence, or empty tuple, as it is referred to. An n-tuple is defined inductively using the construction of an ordered pair.
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Related Research Articles
The relational model (RM) for database management 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 tuples, grouped into relations. A database organized in terms of the relational model is a relational database.
A 'conceptual schema' is a high-level description of a business's informational needs. It typically includes only the main concepts and the main relationships among them Typically this is a first-cut model, with insufficient detail to build an actual database. This level describes the structure of the whole database for a group of users. The conceptual model is also known as the data model that can be used to describe the conceptual schema when a database system is implemented. It hides the internal details of physical storage and targets on describing entities, datatype, relationships and constraints.
The Enterprise Objects Framework, or more commonly simply EOF, was introduced by NeXT in 1994 as a pioneering object-relational mapping product for its NeXTSTEP and OpenStep development platforms. EOF abstracts the process of interacting with a relational database by mapping database rows to Java or Objective-C objects. This largely relieves developers from writing low-level SQL code.
A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to properties of the real world entities. For instance, a data model may specify that the data element representing a car be composed of a number of other elements which, in turn, represent the color and size of the car and define its owner.
First normal form (1NF) is a property of a relation in a relational database. A relation is in first normal form if and only if the domain of each attribute contains only atomic (indivisible) values, and the value of each attribute contains only a single value from that domain. The first definition of the term, in a 1971 conference paper by Edgar Codd, defined a relation to be in first normal form when none of its domains have any sets as elements.
A surrogate key in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data, unlike a natural key which is derived from application data.
WinFS was the code name for a canceled data storage and management system project based on relational databases, developed by Microsoft and first demonstrated in 2003 as an advanced storage subsystem for the Microsoft Windows operating system, designed for persistence and management of structured, semi-structured and unstructured data.
Database design is the organisation of data according to a database model. The designer determines what data must be stored and how the data elements interrelate. With this information, they can begin to fit the data to the database model.
In a relational database, a column is a set of data values of a particular simple type, one value for each row of the database. A column may contain text values, numbers, or even pointers to files in the operating system. Some relational database systems allow columns to contain more complex data types; whole documents, images or even video clips are examples. A column can also be called an attribute.
The associative model of data is a data model for database systems. Other data models, such as the relational model and the object data model, are record-based. These models involve encompassing attributes about a thing, such as a car, in a record structure. Such attributes might be registration, colour, make, model, etc. In the associative model, everything which has “discrete independent existence” is modeled as an entity, and relationships between them are modeled as associations. The granularity at which data is represented is similar to schemes presented by Chen ; Bracchi, Paolini and Pelagatti ; and Senko.
The object-relational impedance mismatch is a set of conceptual and technical difficulties that are often encountered when a relational database management system (RDBMS) is being served by an application program written in an object-oriented programming language or style, particularly because objects or class definitions must be mapped to database tables defined by a relational schema.
Entity–attribute–value model (EAV) is a data model to encode, in a space-efficient manner, entities where the number of attributes that can be used to describe them is potentially vast, but the number that will actually apply to a given entity is relatively modest. Such entities correspond to the mathematical notion of a sparse matrix.
In database relational modeling and implementation, a unique key of a relation is a minimal superkey for that relation; that is, a set of attributes such that:
the relation does not have two distinct tuples with the same values for these attributes
there is no proper subset of these attributes for which (1) holds.
A document-oriented database, or document store, is a computer program designed for storing, retrieving and managing document-oriented information, also known as semi-structured data.
In computing, a graph database (GDB) is a database that uses graph structures for semantic queries with nodes, edges and properties to represent and store data. A key concept of the system is the graph, which directly relates data items in the store a collection of nodes of data and edges representing the relationships between the nodes. The relationships allow data in the store to be linked together directly, and in many cases retrieved with one operation. Graph databases hold the relationships between data as a priority. Querying relationships within a graph database is fast because they are perpetually stored within the database itself. Relationships can be intuitively visualized using graph databases, making it useful for heavily inter-connected data.
The following outline is provided as an overview of and topical guide to databases:
