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Relational Model: The relational model uses a collection of tables to represent both data and the relationships among those data. Each table has multiple columns and each column has a unique name. Figure presents a sample relational database comprising three tables: One shows details of bank customer, the second shows accounts belong to which customers. The relational is an example of a record based model. Record based models are so named because the database is structured in fixed format records of several types. Each table contains of a particular types. Each types defines a fixed number of fields or attributes. The relational data model is the most widely used data model, and a vast majority of current database systems are based on the relational model. The relational model is at a lower level of abstractions than the E-R model.
Other Data Models: The object- oriented data model is another data model that has seen increasing attention. The object- oriented model can be seen as extending the E-R model with notions of encapsulation, methods, and object identity. Historically, two other data models, the network data model and the hierarchical data model, preceded the relation of data model. These models were tied closely to the underlying implementation, and complicated the task of modeling data. Semi structured data models permit the specification of data where indivisible data items of the same type may have different sets of attributes. This is in contrast with the data models mentioned earlier, where every data item of a particular type must have the same set of attributes. The extensible markup language (XML) is widely used to represent semi- structured data.
Keys:
Superkey: It is a set of one or more attributes that taken collectively; allow us to identify an entity set. Candidate key: Superkeys from which no proper subset is a superkey. Such minimal superkeys are called candedate keys.
Primary key: Allows us to distinguish between different entities of set. It must be chosen s.t. its attributes are never or rarely changed.
Foreign Key: When relation schema say r1may include among its attributes the primary key of another relation schema say r2. This attribute is called foreign key from r1, referencing r2, we sometimes define a primary key and sometimes not but there also candidate key will exist. Two attributes taken together can make a key called as composite primary key.
Normalize the given relation to 3NF, justifying each step
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Attributes having a one value for a particular entity. For instance, Age is a single valued attribute of a student entity. Attributes that have more than single values
Define Forms Based Interfaces? Forms-Based Interfaces - A forms-based interface display a form to each user. Forms are commonly designed and programmed for naive users and inte
Create an entity relationship diagram, Database Management System
I want Database Of United Kingdom with Criteria of:\r\n\r\n1). Name, Number, City, State, Postal Code, Address, Email id, DOB.\r\n\r\n2). Unsecure Debts only adds Credit Card Payme
Illustrate how you can use QBE to perform logical AND and OR operation
How are tables stored on Disk? We realise that every record of a table can have different amounts of data. This is due to in some records; some attribute values may be "zero".
What it creates while a primary key is combined with a foreign key? It creates Parent-Child relation ship between the tables that connect them while a primary key is combined w
Write short notes on relational constraints? Relational Constraints are: 1. NOT NULL 2. Unique 3. Primary key 4. Foreign key 5. Table check
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