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Record based Logical Models: Use records as the key data representation components
Examples:
Relational Model: It shows data as well as relationship between data in the form of tables.
Constraints are stored in a meta-data table. This is a very easy model and is based on a proven mathematical theory. This is the most usually used data base model.
Network Model: In this model data is shown as records and relationship as links. A easy network model example is explained in Figure . It shows a sample diagram for such a system. This model is a very good quality model as far as conceptual framework is concerned but is today not used in database management systems.
Write short note on Events Events consist of inputs, interrupts, decisions and actions performed by any external device or users. Every event always has a sender and receiver.
Consider a database schema consisting of four relations, whose schemas are: Product (maker, model, type) PC (model, speed, ram, hd, price) Laptop (model, speed, ram, hd, s
MOSS VALE is a town with 15000 inhabitants. The fire department wishes to develop a system that automates the despatch of fire engines to attend fires. The ERD below describes the
What does the extract statement do in extract datasets? The data is written to virtual memory by extract commands.
Define the term- Actors and Data Stores Actors: An actor is the active object which drives data flow graph by producing or consuming values. Actors are attached to inputs a
Differentiate between B-tree and B + tree Ans: A B-tree (or Balanced Tree) is a search tree along with additional constraints that makes sure that the tree is all the time
In the ER diagram, one example of subclassing is depicted following the Services entity. The subclasses Item Based and Time Based are created. The entity Services gains the attribu
How to create values of structured type? Constructor functions are used to make values of structured types. A function with the similar name as a structured type is a construct
What is key ? Key - A single attribute or a combination of two or more attributes of an entity set which is used to recognize one or more instances (rows) of the set (table) is
State the process of Rearranging Classes and Operations The various, yet similar operation of different classes can be slightly modified thus that they can be covered by a sin
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