Data modeling made simple with powerdesigner take it with. What is the function of etc directory qa answers com. Chapter 8 The Entity Relationship Data ModelData Modeling Made Simple Powerdesigner best way to document database mappings for migrations. This book is written in a conversational style that encourages you to read it from start to finish and master these ten objectives: Know when. Data Modeling Made Simple-Steve Hoberman Data Modeling Made Simple will provide the business or IT professional with a practical working knowledge of data modeling concepts and best practices.1.1.2 Modeling with Ordinary Dierential Equations Although modeling with ordinary dierential equations shares many of the ideas of modeling with the dierence equations discussed above, there are many fundamen-7 Often observed data can be employed to assist in this eort. ER models are readily translated to relations. ER models, also called an ER schema, are represented by ER diagrams.with dierence equations. It is well suited to data modelling for use with databases because it is fairly abstract and is easy to discuss and explain. The entity relationship (ER) data model has existed for over 35 years. Discover and document any data from anywhere for consistency, clarity and artifact reuse across large-scale data integration, master data management, metadata management, Big Data, business intelligence and analytics initiatives all.This database contains information about employees, departments and projects. Ba (entity) teaches (relationship) the Database Systems course (entity).For the rest of this chapter, we will use a sample database called the COMPANY database to illustrate the concepts of the ER model. Relationships, defined as the associations or interactions between entitiesHere is an example of how these two concepts might be combined in an ER data model: Prof.Each employee has a name, identification number, address, salary and birthdate. A department controls a number of projects, each of which has a unique name, a unique number and a budget. Each department has a unique identification, a name, location of the office and a particular employee who manages the department. There are several departments in the company.
Data Modeling Made Simple With Powerdesigner Professional With AAn object with physical existence (e.g., a lecturer, a student, a car) Each dependent has a name, birthdate and relationship with the employee.An entity is an object in the real world with an independent existence that can be differentiated from other objects. We want to keep track of the dependents for each employee. We also need to know the direct supervisor of each employee. We need to record the start date of the employee in each project. A table without a foreign key or a table that contains a foreign key that can contain nulls is a strong entityAnother term to know is entity type which defines a collection of similar entities.An entity set is a collection of entities of an entity type at a particular point of time. Without a corresponding employee record, the spouse record would not exist.An entity is considered strong if it can exist apart from all of its related entities. The Spouse table, in the COMPANY database, is a weak entity because its primary key is dependent on the Employee table. Its primary key is derived from the primary key of the parent entity That is, it cannot exist without a relationship with another entity An entity is considered weak if its tables are existence dependent. The primary key may be simple or composite. They are the building blocks of a database. Kernels have the following characteristics: They are what other tables are based on. Independent entitiesIndependent entities, also referred to as kernels, are the backbone of the database. Brad hudson run faster ebookMany to many relationships become associative tables with at least two foreign keys. They are said to be existence dependent on two or more tables. Dependent entities are used to connect two kernels together. Dependent entitiesDependent entities, also referred to as derived entities, depend on other tables for their meaning. These entities have the following characteristics: The foreign key is used to further identify the characterized table. They typically have a one to many relationship. These entities have the following characteristics: Use a composite of foreign keys and a qualifying columnCharacteristic entities provide more information about another table. Use a composite of foreign keys of associated tables if unique There are three options for the primary key: Data Modeling Made Simple With Powerdesigner Plus A QualifyingIn the COMPANY database, these might include: Create a new simple primary key. Use a composite of foreign key plus a qualifying column Multivalued attributesMultivalued attributes are attributes that have a set of values for each entity. An example of composite attributes. In the COMPANY database, an example of this would be: Name = Figure 8.3. Simple attributesSimple attributes are those drawn from the atomic value domains they are also called single-valued attributes. Later on we will discuss fixing the attributes to fit correctly into the relational model. Age can be derived from the attribute Birthdate. An example of this can be seen in Figure 8.5. Derived attributesDerived attributes are attributes that contain values calculated from other attributes. Example of a multivalued attribute. Candidate keyA candidate key is a simple or composite key that is unique and minimal. These are described below. Types of KeysThere are several types of keys. The key is an attribute or a group of attributes whose values can be used to uniquely identify an individual entity in an entity set. KeysAn important constraint on an entity is the key. Example of a derived attribute. It must uniquely identify tuples in a table and not be null. Last Name and Department ID – assuming two people with the same last name don’t work in the same departmentThe primary key is a candidate key that is selected by the database designer to be used as an identifying mechanism for the whole entity set. Last Name and DepartmentID – assuming two people with the same last name don’t work in the same departmentA composite key is composed of two or more attributes, but it must be minimal.Using the example from the candidate key section, possible composite keys are: First Name and Last Name – assuming there is no one else in the company with the same name It is minimal because every column is necessary in order to attain uniqueness.From our COMPANY database example, if the entity is Employee(EID, First Name, Last Name, SIN, Address, Phone, BirthDate, Salary, DepartmentID), possible candidate keys are: Msi backup recovery windows 10Foreign keyA foreign key (FK) is an attribute in a table that references the primary key in another table OR it can be null. Alternate keyAlternate keys are all candidate keys not chosen as the primary key. This key is indicated by underlining the attribute in the ER model.In the following example, EID is the primary key:Employee( EID, First Name, Last Name, SIN, Address, Phone, BirthDate, Salary, DepartmentID) Secondary keyA secondary key is an attribute used strictly for retrieval purposes (can be composite), for example: Phone and Last Name. This is referred to as the primary key. A key is chosen by the database designer to be used as an identifying mechanism for the whole entity set. A candidate key is selected by the designer to uniquely identify tuples in a table.
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