14ġ5 OODBMS or ORDBMS? OODBMS put more emphasis on the role of the client side This can improve long, process intensive, transactions. Locking at object-level impacts performance Complexity Lack of support for views Lack of support for security 10ġ1 Then What is an ORDBMS? An Object-Relational database adds features associated with objectoriented systems to a RDBMS OR Extend the relational data model by including object orientation and constructs to deal with added data types 11ġ2 Object-Relational DBMS Features OODBS support noted by RDBMS vendors include User-extensible type system Encapsulation Inheritance Polymorphism Dynamic binding of methods Complex objects including first normal form objects Object Identity 12ġ3 ORDBMS Drawbacks Disadvantages of ORDBMS Complexity Increased costs Unclear if the ORDBMS will actually combine relationships and encapsulated objects to correctly and completely mirror the real world Provision of a language(s) which will front end to SQL and will provide a migration path for existing SQL users 13ġ4 ORDBMS-SQ元 SQ元 is a superset of SQL/92, in that it supports all of the constructs supported by that standard, as well as adding new ones of its own. 9ġ0 OODBMS Disadvantages Lack of a universal data model? Ad-hoc querying compromises encapsulation. Applicable for advanced database applications Improved performance. The RDBMS has domains, keys, multi-valued and join dependencies 5Ħ OODBMS Architecture OBJECT ORIENTED DATABASE MANAGEMENT SYSTEM OOPL Complex Objects Object Identity Methods & Messages Inheritance Polymorphism Extensibility Computational Completeness DBMS Persistence Disc Management Data Sharing Reliability Security Ad Hoc Querying 6ħ OODBMS Main Features Complex objects Object Identity Encapsulation Classes Inheritance Overriding and late-binding Extensibility Computational completeness Persistence Concurrency Recovery Ad-hoc querying 7Ĩ Storage-Levels RDBMS Storage ODBMS Storage Main or virtual memory Secondary storage Transforming and type checking SQL Main or virtual memory Secondary storage 8ĩ OODBMS Advantages Enriched modelling capabilities Extensibility Support for schema evolution. This compounds on the join feature of query processing The many to many relationship is difficult to express. 4ĥ Relational DBMS Limitations Normalisation (Normal Forms and FDs) sometimes lead to relations which do not exist, or correspond, to entities in the real world. Poor representation of real world entities Poor support for integrity & business constraints. 2 Database Models Transition Hierarchical Data Model Network Data Model Relational Data Model ER Data Model Semantic Data Model Object-Relational DM Object-Oriented DM 2ģ Main Issues Relational DBMS Limitations What is an OODBMS? Advantages and Disadvantages of OODBMS What is an ORDBMS? What is SQ元? Comparison of OODBMS and ORDBMS When to use an OODBMS When to use an ORDBMS 3Ĥ Relational DBMS Limitations Semantic overloading.
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