In today's world, Client-Server applications that rely on a database on the server as a data store while servicing requests from multiple clients are quite commonplace.
This causes a certain inefficency as objects must be mapped to tuples in the database and vice versa instead of the data being stored in a way that is consistent with the programming model.
The "impedance mismatch" caused by having to map objects to tables and vice versa has long been accepted as a necessary performance penalty.
This paper is aimed at seeking out an alternative that avoids this penalty. Object oriented programming concepts such as encapsulation, polymorphism and inheritance are enforced as well as database management concepts such as the ACID properties Atomicity, Consistency, Isolation and Durability which lead to system integrity, support for an ad hoc query language and secondary storage management systems which allow for managing very large amounts of data.
From the aforementioned description, an OODBMS should be able to store objects that are nearly indistinguishable from the kind of objects supported by the target programming language with as little limitation as possible.
Persistent objects should belong to a class and can have one or more atomic types or other objects as attributes. The normal rules of inheritance should apply with all their benefits including polymorphism, overridding inherited methods and dynamic binding.
An object-oriented database management system (OODBMS), sometimes shortened to ODBMS for object database management system), is a database management system that supports the modelling and creation of data as objects. When you integrate database capabilities with object programming language capabilities, the result is an object-oriented database management system or ODBMS. 1 An ODBMS makes database objects appear as programming language objects in one or more existing programming languages. Object database management systems extend the . An object-oriented database management system (OODBMS) is a database management system that supports the creation and modeling of data as objects. OODBMS also includes support for classes of objects and the inheritance of class properties, and incorporates methods, subclasses and their objects.
Each object has an object identifier OID which used as a way of uniquely identifying a particuler object. OIDs are permanent, system generated and not based on any of the member data within the object.
OIDs make storing references to other objects in the database simpler but may cause referential intergrity problems if an object is deleted while other objects still have references to its OID. Features that are common in the RDBMS world such as transactions, the ability to handle large amounts of data, indexes, deadlock detection, backup and restoration features and data recovery mechanisms also exist in the OODBMS world.
A primary feature of an OODBMS is that accessing objects in the database is done in a transparent manner such that interaction with persistent objects is no different from interacting with in-memory objects. Database operations typically involve obtaining a database root from the the OODBMS which is usually a data structure like a graph, vector, hash table, or set and traversing it to obtain objects to create, update or delete from the database.
A relation or table in a relational database can be considered to be analogous to a class in an object database. A tuple is similar to an instance of a class but is different in that it has attributes but no behaviors.
A column in a tuple is similar to a class attribute except that a column can hold only primitive data types while a class attribute can hold data of any type.
Finally classes have methods which are computationally complete meaning that general purpose control and computational structures are provided [McF 99] while relational databases typically do not have computationally complete programming capabilities although some stored procedure languages come close.
Advantages Composite Objects and Relationships: It is thus possible to have a large class which holds many medium sized classes which themselves hold many smaller classes, ad infinitum.
In a relational database this has to be done either by having one huge table with lots of null fields or via a number of smaller, normalized tables which are linked via foreign keys. Having lots of smaller tables is still a problem since a join has to be performed every time one wants to query data based on the "Has-a" relationship between the entities.
Also an object is a better model of the real world entity than the relational tuples with regards to complex objects. Data in the real world is usually has hierarchical characteristics.
An Employee can be a Manager or not, this is usually done in an RDBMS by having a type identifier field or creating another table which uses foreign keys to indicate the relationship between Managers and Employees. Circumventing the Need for a Query Language: In a typical application that uses an object oriented programming language and an RDBMS, a signifcant amount of time is usually spent mapping tables to objects and back.
There are also various problems that can occur when the atomic types in the database do not map cleanly to the atomic types in the programming language and vice versa. The user of an RDBMS has to worry about uniquely identifying tuples by their values and making sure that no two tuples have the same primary key values to avoid error conditions.
Thus there is no limitation on the values that can be stored in an object. A data model typically should model entities and their relationships, constraints and operations that change the states of the data in the system.
With an RDBMS it is not possible to model the dynamic operations or rules that change the state of the data in the system because this is beyond the scope of the database.
Thus applications that use RDBMS systems usually have an Entity Relationship diagram to model the static parts of the system and a seperate model for the operations and behaviors of entities in the application.
With an OODBMS there is no disconnect between the database model and the application model because the entities are just other objects in the system.
An entire application can thus be comprehensively modelled in one UML diagram. In an RDBMS modifying the database schema either by creating, updating or deleting tables is typically independent of the actual application.
In an OODBMS based application modifying the schema by creating, updating or modifying a persistent class typically means that changes have to be made to the other classes in the application that interact with instances of that class.
Also updating all the instance objects within the database can take an extended period of time depending on the size of the database. Lack of Ad-Hoc Queries: In an RDBMS, the relational nature of the data allows one to construct ad-hoc queries where new tables are created from joining existing tables then querying them.
Since it is currently not possible to duplicate the semantics of joining two tables by "joining" two classes then there is a loss of flexibility with an OODBMS.
Its product, Selector, automates the needs of the entire radio station -- from the music library, to the newsroom, to the sales department. The production data is distributed across several hundred processing nodes and over 30 on-line servers.
Compare the size of the code in both examples.A Database Management System (DBMS) is an important software system used extensively throughout the computer industry. As for other major software systems, such as compilers and operating systems.
An object-oriented database management system (OODBMS), sometimes shortened to ODBMS for object database management system), is a database management system that supports the modelling and creation of data as objects.
An object-oriented database management system (OODBMS, but sometimes just called “object database”) is a DBMS that stores data in a logical model that is closely aligned with an application program’s object model. An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming.
Object databases are different from relational databases which are table-oriented. Object-relational databases are a hybrid of both approaches. Definition An object database management system (ODBMS, also referred to as object-oriented database management system or OODBMS), is a database management system (DBMS) that supports the modelling and creation of data as objects.
Object oriented programming concepts such as encapsulation, polymorphism and inheritance are enforced as well as database management concepts such as the ACID properties (Atomicity, Consistency, Isolation and Durability) which lead to system integrity, support for an ad hoc query language and secondary storage management systems .
Object oriented programming concepts such as encapsulation, polymorphism and inheritance are enforced as well as database management concepts such as the ACID properties (Atomicity, Consistency, Isolation and Durability) which lead to system integrity, support for an ad hoc query language and secondary storage management systems which allow for managing very large amounts . When you integrate database capabilities with object programming language capabilities, the result is an object-oriented database management system or ODBMS. 1 An ODBMS makes database objects appear as programming language objects in one or more existing programming languages. Object database management systems extend the . 1 Object Database Management Systems (ODBMSs) CSC – Fall * Notes kindly borrowed from D R AZIZ AIT-BRAHAM, School of Computing, IS & Math, South Bank University 2 Evolution and Definition of the ODBMS.