A simple attribute (or atomic) is one cannot be broken down any further.Ī stored attribute is one which data is input it may be left blank on creation, to be entered later.Ī derived attribute is one whose values may be calculated from related attribute values, or data not stored in the database, or attributes from other entities that are related.Īn identifier is an attribute or combination of which periods which uniquely identify individual instances of entity type. The decision whether or not to divide an attribute into composite attributes depends on whether or not the data is necessary at that level. This is referred to as a composite attribute.
#Associative entity navicat data modeler zip
For example, the address attribute in the entity type student may be broken: street address, apartment, city, state, zip code. Some attributes can be further broken down.
#Associative entity navicat data modeler plus
Each entity has an identifying attribute plus other attributes which further describe the entity type. For example, a student entity type might have the attributes: student ID, student name, address, phone number, major, grade-point average, date of enrollment.Įach entity instance has a value associated with each of the attributes of that entity type. An attribute is a property or characteristic of an entity type. The relationship between a weak entity type and its owner is called an identifying relationship.Įach entity type has a set of attributes associative with it. The double blocks and double diamond indicate weak relationship. Explain the example on page 93, figure 3 - 5. A strong entity type is one that exists independently of other entity types, meaning that it should always have an identifier, that which uniquely distinguishes each entity instance.Ī weak entity type is one whose existence depends on another entity type.Ī weak entity type does not have its own identifier, but rather a partial identifier that that relies on an identifier from another entity type. Most of your basic entity types should be strong entity types. Go over inappropriate entity usage on page 92. Entity type is metadata, entity instance is the data. An entity instance of an entity type is the actual data for example, an employee might be the entity type, an entity instance might be a specific employee. The entity type is given a name and placed inside of a rectangle. Some examples are: a person (employee, student ) a place (city, state) object (building, computer) event (sale, class registration) concept (account, class course).Īn entity type is a collection of entities that's share common characteristics or properties, and is given a name. The simplistic yet powerful model allows accurate real world constructs.Īn entity is a person, place, object, event, or concept about which the business or organization wishes to maintain data. The basic constructs of an entity relationship model are entities, relationships, and attributes. 87.Įntity relationship model constructs, p. Go over sample entity relationship diagram, figure 3.1, p. The entity relationship model is expressed in terms of entities, relationships among those entities,Īnd the attributes of both the entities and their relationships. 87).Īn entity relationship diagram is a graphical representation of an entity relationship model. Defining flow of data enables maximum flexibility for information.ĭefined as a logical representation of the data for a business process (p.For example, accounting processes may change but not the data that flows into the process. While process flow may be unstable over a long period of time, data flow tends to have a longer lifespan. Capturing the flow of data through a process provides independence from those processes.The facts and rules captured during data modeling to help ensure data integrity. Data characteristics understood during data modeling are crucial to design.The conceptual data model that is the most popular is the entity relationship or ER model. Represents entities and relationships as represented in the real world. In other words, the conceptual data model We must represent a conceptual data model, which is independent of any technologyīut rather the business process in humanistic terms. The first step in database development is database analysis. Lecture notes chapter 3: the entity relationship model
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