What are the benefits of using Abstract Data Types?

Answer 1

• The implementor of the class can change the implementation for maintenance, bug fixes or optimization reasons, without disturbing the client code.
• The data type is defined as a set of high-level services with a semantic contract defining both the output that is provided and the input that is required from the client. This actually correspond to the general definition of a type in programming: a type is defined as a set of possible values and a set of operations available on these values.

Answer 2

1. Encapsulation - Because each user-defined data type exist as a complete entity, including the data definitions, default values, and value constraints, this entity insures uniformity and consistency. Once defined, a user-defined data type may participate in many other user-defined data types, such that the same logical data type, always has the same definition, default values and value constraints, regardless of where it appears in the database.

2. Reusability - As a hierarchy of common data structures are assembled, these can be re-used within many definitions, saving coding time and insuring uniformity.

3. Flexibility - The ability to create real-world data representations of data allows the database object designer to model the real world as it exists.

As you can see there are many compelling reasons to have user-defined data typing, provided that the data types are properly analyzed and incorporated into the database object model. Let's take a look at some of the implementation issues that relate to the object model and data typing.

Nesting of user-defined data types

Now lets take this concept one step further and consider how user-defined data types can be nested within other data types. A basic example, would be to create a data type that would encapsulate all of the data in a table:

CREATE TYPE customer_stuff (

full_name customer_name,

home_address customer_address

business_address customer_address);

With the customer_stuff type defined, table definition becomes simple:

CREATE TABLE CUSTOMER (customer_data customer_stuff);

Using this type of user-defined data type we are essentially duplicating the object-oriented concept of encapsulation. That is, we are placing groups of related data types into a container that is completely self-contained and has the full authority of the innate relational data types such as int and char.

Select customer_stuff.customer_name.zip_code

from customer

where customer_stuff.customer_name.zip_code like '144%';

Manipulating ADT's

In many object databases it is possible to directly retrieve and pass an abstract data type. While this is a matter of convenience for most programmers, there are some very useful applications of this technique, especially for the object/relational databases. In object/relational databases, ADT's can be directly retrieved and used inside other tables. In the following Oracle example, a new table called good_customer is created by retrieving the entire ADT from the customer table

Answer 3

Abstract data types does not have any maximum reservable memory allocation size and also has no limit in storing the size and types of variables like primitive data types.

They can stores all the characters of Unicode and also allocate space in memory according to the size of the variable given by the user each time.

Answer 4

Because there is no existing type of data that can be used for that purpose.