Encapsulation of operations, methods & persistence
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The document discusses encapsulation in programming, emphasizing its role in binding data and functions while hiding implementation details from external users. It explains the application of encapsulation in database objects, highlighting operations for creating and deleting objects, and the distinction between visible and hidden attributes. Additionally, it covers the concept of persistence in object-oriented programming, differentiating between transient and persistent objects, and introduces mechanisms for achieving persistence through naming and reachability.
Encapsulation of operations, methods & persistence
- 1. Encapsulation of Operations, Methods & Persistence BY PREM LAMSAL 31 BSC.CSIT 7TH SEMESTER
- 2. Encapsulation Encapsulation is related to the concepts of abstract data types and information hiding in programming languages. Encapsulation is a mechanism of binding data with functions.
- 3. Encapsulation of Operations The concepts of encapsulation is applied to database objects in ODBs by defining the behavior of a type of object based on the operations that can be externally applied to objects of that type. Some operations may be used to create (insert) or destroy (delete) The external users of the object are only made aware of the interface of the operations, which defines the name and arguments (parameters) of each operation. The implementation is hidden from the external users.
- 4. Encapsulation of Operations For database applications, the requirement that all objects be completely encapsulated is too stringent. One way to relax this requirement is to divide the structure of an object into visible and hidden attributes (instance variables). Visible attributes can be seen by and are directly accessible to the database users and programmers via the query language. The hidden attributes of an object are completely encapsulated and can be accessed only through predefined operations. Most ODMSs employ high-level query languages for accessing visible attributes.
- 6. Persistence The OOPL is used to specify the method (operation) implementations as well as other application code. Not all objects are meant to be stored permanently in the database. Transient objects exist in the executing program and disappear once the program terminates. Persistent objects are stored in the database and persist after program termination. The typical mechanisms for making an object persistent are naming and reachability.
- 7. Persistence The naming mechanism involves giving an object a unique persistent name within a particular database. This persistence object name can be given via a specific statement or operation in the program The named persistent objects are used as entry points to the database through which users and applications can start their database access. It is not practical to give name to all object in large database in thousands of objects so, some objects are made persistence using second mechanism called reachability.
- 8. Persistence : Reachability The reachability mechanism works by making the object reachable from some other persistent object. An object B is said to be reachable from an object A if a sequence of references in the database lead from object A to object B. If we first create a named persistent object N, whose state is a set (or possibly a bag) of objects of some class C, we can make objects of C persistent by adding them to the set, thus making them reachable from N. Hence, N is a named object that defines a persistent collection of objects of class C. In the object model standard, N is called the extent of C.
- 9. Persistence
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