In this chapter we will talk about Abstract Data Types. This time it was presented by our friend’s group. This session is divided into some topics that as we can see below.
- The Concept of Abstraction
- Introduction to Data Abstraction
- Language Examples
- Parameterized Abstract Data Types
- Encapsulation Constructs
- Naming Encapsulations
The first topic is about The Concept of Abstraction. In this topic we learned that An abstraction is a view or representation of an entity that includes only the most significant attributes. In a general sense, abstraction allows one to collect instances of entities into groups in which their common attributes need not be considered. In the world of programming languages, abstraction is a weapon against the complexity of programming; its purpose is to simplify the programming process. It is an effective weapon because it allows programmers to focus on essential attributes, while ignoring subordinate attributes. Let’s move on to the next topic about Introduction to Data Abstraction, Syntactically, an abstract data type is an enclosure that includes only the data representation of one specific data type and the subprograms that provide the operations for that type. Through access controls, unnecessary details of the type can be hidden from units outside the enclosure that use the type. Program units that use an abstract data type can declare variables of that type, even though the actual representation is hidden from them. An instance of an abstract data type is called an object . We learned that Object-oriented programming is an outgrowth of the use of data abstraction in software development, and data abstraction is one of its fundamental components. Next, we will discuss the language examples, C++, which was first released in 1985, was created by adding features to C. The first important additions were those to support object-oriented programming. Because one of the primary components of object-oriented programming is abstract data types, C++ obviously is required to support them. While Ada provides an encapsulation that can be used to simulate abstract data types, C++ provides two constructs that are very similar to each other, the class and the struct, which more directly support abstract data types. Because structs are most commonly used when only data is included, we do not discuss them further here
Next topic is about Parameterized Abstract Data Types.We learned that It is often convenient to be able to parameterize abstract data types. For example, we should be able to design a stack abstract data type that can store any scalar type elements rather than be required to write a separate stack abstraction for every different scalar type. Note that this is only an issue for static typed languages. In a dynamic typed language like Ruby, any stack implicitly can store any type elements. Next topic is about Encapsulation Constructs, C does not provide complete support for abstract data types, although both abstract data types and multiple-type encapsulations can be simulated. In C, a collection of related functions and data definitions can be placed in a file, which can be independently compiled. Such a file, which acts as a library, has an implementation of its entities. The interface to such a file, including data, type, and function declarations, is placed in a separate file called a header file. Type representations can be hidden by declaring them in the header file as pointers to struct types. Move to next topic there’s Naming Encapsulations. Naming encapsulations define name scopes that assist in avoiding these name conflicts. Each library can create its own naming encapsulation to prevent its names from conflicting with the names defined in other libraries or in client code. Each logical part of a software system can create a naming encapsulation with the same purpose. Naming encapsulations are logical encapsulations, in the sense that they need not be contiguous. Several different collections of code can be placed in the same namespace, even though they are stored in different places.
