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Many-to-one
In systems analysis, a one-to-many relationship is a type of cardinality (data modeling), cardinality that refers to the relationship between two wikt:entity, entities (see also entity–relationship model). For example, take a car and an owner of the car. The car can only be owned by one owner at a time or not owned at all, and an owner could own zero, one, or multiple cars. One owner could have many cars, one-to-many. In a relational database, a one-to-many relationship exists when one record is related to many records of another table. A one-to-many relationship is not a property of the data, but rather of the relationship itself. One-to-many often refer to a primary key to foreign key relationship between two tables, where the record in the first table can relate to multiple records in the second table. A foreign key is one side of the relationship that shows a row or multiple rows, with one of those rows being the primary key already listed on the first table. This is also cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardinality (data Modeling)
Within data modelling, cardinality is the numerical relationship between rows of one table and rows in another. Common cardinalities include ''one-to-one'', ''one-to-many'', and ''many-to-many''. Cardinality can be used to define data models as well as analyze entities within datasets. Relationships For example, consider a database of electronic health records. Such a database could contain tables like the following: * A doctor table with information about physicians. * A patient table for medical subjects undergoing treatment. * An appointment table with an entry for each hospital visit. Natural relationships exist between these entities: * A many-to-many relationship between records in doctor and records in patient because doctors have many patients and patients can see many doctors. * A one-to-many relationship between records in patient and records in appointment because patients can have many appointments and each appointment involves only one patient. * A one-to-one rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Systems Analysis
Systems analysis is "the process of studying a procedure or business to identify its goal and purposes and create systems and procedures that will efficiently achieve them". Another view sees systems analysis as a problem-solving technique that breaks a system down into its component pieces and analyses how well those parts work and interact to accomplish their purpose. The field of system analysis relates closely to requirements analysis or to operations research. It is also "an explicit formal inquiry carried out to help a decision maker identify a better course of action and make a better decision than they might otherwise have made." The terms analysis and synthesis stem from Greek, meaning "to take apart" and "to put together", respectively. These terms are used in many scientific disciplines, from mathematics and logic to economics and psychology, to denote similar investigative procedures. The analysis is defined as "the procedure by which we break down an intellectual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entity
An entity is something that Existence, exists as itself. It does not need to be of material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is Life, animate, or present. The verb tense of this form is to 'entitize' - meaning to convert into an entity; to perceive as tangible or alive. The term is broad in scope and may refer to animals; natural features such as mountains; inanimate objects such as tables; numbers or sets as symbols written on a paper; human contrivances such as laws, corporations and academic disciplines; or supernatural beings such as gods and spirits. The adjectival form is ''entitative''. Etymology The word ''entity'' is derived from the Latin ''entitas'', which in turn derives from the Latin ''ens'' meaning "being" or "existing" (compare English ''essence''). ''Entity'' may hence literally be taken to mean "thing which exists". In philosophy Ontology is th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entity–relationship Model
An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between entities (instances of those entity types). In software engineering, an ER model is commonly formed to represent things a business needs to remember in order to perform business processes. Consequently, the ER model becomes an abstract data model, that defines a data or information structure that can be implemented in a database, typically a relational database. Entity–relationship modeling was developed for database and design by Peter Chen and published in a 1976 paper, with variants of the idea existing previously. Today it is commonly used for teaching students the basics of database structure. Some ER models show super and subtype entities connected by generalization-specialization relationships, and an ER model can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relational Database
A relational database (RDB) is a database based on the relational model of data, as proposed by E. F. Codd in 1970. A Relational Database Management System (RDBMS) is a type of database management system that stores data in a structured format using rows and columns. Many relational database systems are equipped with the option of using SQL (Structured Query Language) for querying and updating the database. History The concept of relational database was defined by E. F. Codd at IBM in 1970. Codd introduced the term ''relational'' in his research paper "A Relational Model of Data for Large Shared Data Banks". In this paper and later papers, he defined what he meant by ''relation''. One well-known definition of what constitutes a relational database system is composed of Codd's 12 rules. However, no commercial implementations of the relational model conform to all of Codd's rules, so the term has gradually come to describe a broader class of database systems, which at a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Foreign Key
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those attributes must also be a candidate key in S. In other words, a foreign key is a set of attributes that a candidate key. For example, a table called TEAM may have an attribute, MEMBER_NAME, which is a foreign key referencing a candidate key, PERSON_NAME, in the PERSON table. Since MEMBER_NAME is a foreign key, any value existing as the name of a member in TEAM must also exist as a person's name in the PERSON table; in other words, every member of a TEAM is also a PERSON. Summary The table containing the foreign key is called the child table, and the table containing the candidate ke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Converse Relation
In mathematics, the converse of a binary relation is the relation that occurs when the order of the elements is switched in the relation. For example, the converse of the relation 'child of' is the relation 'parent of'. In formal terms, if X and Y are sets and L \subseteq X \times Y is a relation from X to Y, then L^ is the relation defined so that yL^x if and only if xLy. In set-builder notation, :L^ = \. Since a relation may be represented by a logical matrix, and the logical matrix of the converse relation is the transpose of the original, the converse relation is also called the transpose relation. It has also been called the opposite or dual of the original relation, the inverse of the original relation,Gerard O'Regan (2016): ''Guide to Discrete Mathematics: An Accessible Introduction to the History, Theory, Logic and Applications'' or the reciprocal L^ of the relation L. Other notations for the converse relation include L^, L^, \breve, L^, or L^. The notati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peter Chen
Peter Pin-Shan Chen (; born 3 January 1947) is a Taiwanese-American computer scientist and applied mathematician. He is a retired distinguished career scientist and faculty member at Carnegie Mellon University and Distinguished Chair Professor Emeritus at Louisiana State University. He is known for the development of the entity–relationship model in 1976. Biography Born in Taichung, Taiwan, Chen received a Bachelor of Science (B.S.) in electrical engineering in 1968 from National Taiwan University and earned a Ph.D. in computer science and applied mathematics at Harvard University in 1973. In 1970, he worked one summer at IBM. After graduating from Harvard, he spent one year at Honeywell and a summer at Digital Equipment Corporation. From 1974 to 1978 Chen was an assistant professor at the MIT Sloan School of Management. From 1978 to 1983 he was an associate professor at the University of California, Los Angeles (UCLA Management School). From 1983 to 2011 Chen held the posi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
One-to-one (data Model)
In systems analysis, a one-to-one relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model) A and B in which one element of A may only be linked to one element of B, and vice versa. In mathematical terms, there exists a bijective function from A to B. For instance, think of A as the set of all human beings, and B as the set of all their brains. Any person from A can and must have only one brain from B, and any human brain in B can and must belong to only one person that is contained in A. In a relational database, a one-to-one relationship exists when one row in a table may be linked with only one row in another table and vice versa. It is important to note that a one-to-one relationship is not a property of the data, but rather of the relationship itself. A list of mothers and their children may happen to describe mothers with only one child, in which case one row of the mothers table will refer to only one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Many-to-many (data Model)
In systems analysis, a many-to-many relationship is a type of cardinality that refers to the relationship between two entities, say, A and B, where A may contain a parent instance for which there are many children in B and vice versa. Data relationships For example, think of A as Authors, and B as Books. An Author can write several Books, and a Book can be written by several Authors. In a relational database management system, such relationships are usually implemented by means of an associative table (also known as join table, junction table or ''cross-reference table''), say, AB with two one-to-many relationships and . In this case the logical primary key for AB is formed from the two foreign keys (i.e. copies of the primary keys of A and B). In web application frameworks such as CakePHP and Ruby on Rails, a many-to-many relationship between entity types represented by logical model database tables is sometimes referred to as a HasAndBelongsToMany (HABTM) relationship. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
