List six major steps that you would take in setting up a database for a particular enterprise.

Answer: Six major steps in setting up a database for a particular enterprise are:

•  Define the high level requirements of the enterprise (this step generates a document known as the system requirements specification.)


•  Define a model containing all appropriate types of data and data relationships.


•  Define the integrity constraints on the data.


•  Define the physical level.


•  For each known problem to be solved on a regular basis (e.g., tasks to be carried out by clerks or Web users) define a user interface to carry out the task, and write the necessary application programs to implement the user interface.


• Create/initialize the database.

Q) Consider a two-dimensional integer array of size n × m that is to be used in your favorite programming language. Using the array as an example, illustrate the difference

(a) between the three levels of data abstraction, and

(b) between a schema and instances.

Answer: Let tgrid be a two-dimensional integer array of size n × m.

a.

•  The physical level would simply be m × n (probably consecutive) storage locations of whatever size is specified by the implementation (e.g., 32 bits each).


•  The conceptual level is a grid of boxes, each possibly containing an integer, which is n boxes high by m boxes wide.


•  There are 2m×n possible views. For example, a view might be the entire array, or particular row of the array, or all n rows but only columns 1 through i.

b.

• Consider the following Pascal declarations:

type tgrid = array[1..n, 1..m] of integer;
var vgrid1, vgrid2 : tgrid

Then tgrid is a schema, whereas the value of variables vgrid1 and vgrid2 are instances.

• To illustrate further, consider the schema array[1..2, 1..2] of integer. Two instances of this scheme are:

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