Object database

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An object database (also object-oriented database) is a database model in which information is represented in the form of objects as used in object-oriented programming.

Example of an Object-Oriented Model.[1]

Object databases are generally recommended when there is a business need for high performance processing on complex data.


[edit] Overview

When database capabilities are combined with object programming language capabilities, the result is an object database management system (ODBMS). An ODBMS makes database objects appear as programming language objects in one or more object programming languages. An ODBMS extends the programming language with transparently persistent data, concurrency control, data recovery, associative queries, and other capabilities.

Some object-oriented databases are designed to work well with object-oriented programming languages such as Python, Java, C#, Visual Basic .NET, C++, Objective-C and Smalltalk; others have their own programming languages. ODBMSs use exactly the same model as object-oriented programming languages.

[edit] History

Object database management systems grew out of research during the early to mid-1970s into having intrinsic database management support for graph-structured objects. The term "object-oriented database system" first appeared around 1985.[citation needed] Notable research projects included Encore-Ob/Server (Brown University), EXODUS (University of Wisconsin-Madison), IRIS (Hewlett-Packard), ODE (Bell Labs), ORION (Microelectronics and Computer Technology Corporation or MCC), Vodak (GMD-IPSI), and Zeitgeist (Texas Instruments). The ORION project had more published papers than any of the other efforts. Won Kim of MCC compiled the best of those papers in a book published by The MIT Press.[2]

Early commercial products included Gemstone (Servio Logic, name changed to GemStone Systems), Gbase (Graphael), and Vbase (Ontologic). The early to mid-1990s saw additional commercial products enter the market. These included ITASCA (Itasca Systems), Jasmine (Fujitsu, marketed by Computer Associates), Matisse (Matisse Software), Objectivity/DB (Objectivity, Inc.), ObjectStore (Progress Software, acquired from eXcelon which was originally Object Design), ONTOS (Ontos, Inc., name changed from Ontologic), O2[3] (O2 Technology, merged with several companies, acquired by Informix, which was in turn acquired by IBM), POET (now FastObjects from Versant which acquired Poet Software), Versant Object Database (Versant Corporation) and VOSS (Logic Arts). Some of these products remain on the market and have been joined by new open source and commercial products such as InterSystems CACHÉ (see the product listings below).

Object database management systems added the concept of persistence to object programming languages. The early commercial products were integrated with various languages: GemStone (Smalltalk), Gbase (LISP), Vbase (COP) and VOSS (Virtual Object Storage System for Smalltalk). For much of the 1990s, C++ dominated the commercial object database management market. Vendors added Java in the late 1990s and more recently, C#.

Starting in 2004, object databases have seen a second growth period when open source object databases emerged that were widely affordable and easy to use, because they are entirely written in OOP languages like Smalltalk, Java or C#, such as db4o (db4objects), DTS/S1 from Obsidian Dynamics and Perst (McObject), available under dual open source and commercial licensing.

[edit] Adoption of object databases

Object databases based on persistent programming acquired a niche in application areas such as engineering and spatial databases, telecommunications, and scientific areas such as high energy physics and molecular biology. They have made little impact on mainstream commercial data processing, though there is some usage in specialized areas of financial services.[citation needed] It is also worth noting that object databases held the record for the World's largest database (being the first to hold over 1000 terabytes at Stanford Linear Accelerator Center)[4] and the highest ingest rate ever recorded for a commercial database at over one Terabyte per hour.

Another group of object databases focuses on embedded use in devices, packaged software, and real-time systems.

[edit] Technical features

Most object databases also offer some kind of query language, allowing objects to be found by a more declarative programming approach. It is in the area of object query languages, and the integration of the query and navigational interfaces, that the biggest differences between products are found. An attempt at standardization was made by the ODMG with the Object Query Language, OQL.

Access to data can be faster because joins are often not needed (as in a tabular implementation of a relational database). This is because an object can be retrieved directly without a search, by following pointers. (It could, however, be argued that "joining" is a higher-level abstraction of pointer following.)

Another area of variation between products is in the way that the schema of a database is defined. A general characteristic, however, is that the programming language and the database schema use the same type definitions.

Multimedia applications are facilitated because the class methods associated with the data are responsible for its correct interpretation.

Many object databases, for example VOSS, offer support for versioning. An object can be viewed as the set of all its versions. Also, object versions can be treated as objects in their own right. Some object databases also provide systematic support for triggers and constraints which are the basis of active databases.

The efficiency of such a database is also greatly improved in areas which demand massive amounts of data about one item. For example, a banking institution could get the user's account information and provide them efficiently with extensive information such as transactions, account information entries etc. The Big O Notation for such a database paradigm drops from O(n) to O(1), greatly increasing efficiency in these specific cases.

[edit] Standards

The Object Data Management Group (ODMG) was a consortium of object database and object-relational mapping vendors, members of the academic community, and interested parties. Its goal was to create a set of specifications that would allow for portable applications that store objects in database management systems. It published several versions of its specification. The last release was ODMG 3.0. By 2001, most of the major object database and object-relational mapping vendors claimed conformance to the ODMG Java Language Binding. Compliance to the other components of the specification was mixed.[5] In 2001, the ODMG Java Language Binding was submitted to the Java Community Process as a basis for the Java Data Objects specification. The ODMG member companies then decided to concentrate their efforts on the Java Data Objects specification. As a result, the ODMG disbanded in 2001.

Many object database ideas were also absorbed into SQL:1999 and have been implemented in varying degrees in object-relational database products.

In 2005 Cook, Rai, and Rosenberger proposed to drop all standardization efforts to introduce additional object-oriented query APIs but rather use the OO programming language itself, i.e., Java and .NET, to express queries. As a result, Native Queries emerged. Similarly, Microsoft announced Language Integrated Query (LINQ) and DLINQ, an implementation of LINQ, in September 2005, to provide close, language-integrated database query capabilities with its programming languages C# and VB.NET 9.

In February 2006, the Object Management Group (OMG) announced that they had been granted the right to develop new specifications based on the ODMG 3.0 specification and the formation of the Object Database Technology Working Group (ODBT WG). The ODBT WG plans to create a set of standards that incorporates advances in object database technology (e.g., replication), data management (e.g., spatial indexing), and data formats (e.g., XML) and to include new features into these standards that support domains where object databases are being adopted (e.g., real-time systems).

On January of 2007 the World wide web Consortium gave final recommendation status to the XQuery language. XQuery has enabled a new class of applications that managed hierarchical data built around the XRX web application architecture that also provide many of the advantages of object databases. In addition XRX applications benefit by transporting XML directly to client applications such as XForms without changing data structures.

[edit] Advantages and disadvantages

Benchmarks between ODBMSs and RDBMSs have shown that an ODBMS can be clearly superior for certain kinds of tasks. The main reason for this is that many operations are performed using navigational rather than declarative interfaces, and navigational access to data is usually implemented very efficiently by following pointers.[6]

Critics of navigational database-based technologies like ODBMS suggest that pointer-based techniques are optimized for very specific "search routes" or viewpoints. However, for general-purpose queries on the same information, pointer-based techniques will tend to be slower and more difficult to formulate than relational. Thus, navigation appears to simplify specific known uses at the expense of general, unforeseen, and varied future uses.[citation needed] However, with suitable language support, direct object references may be maintained in addition to normalised, indexed aggregations, allowing both kinds of access; furthermore, a persistent language may index aggregations on whatever its content elements return from a call to some arbitrary object access method, rather than only on attribute value, which allows a query to 'drill down' into complex data structures.

Other things that work against ODBMS seem to be the lack of interoperability with a great number of tools/features that are taken for granted in the SQL world, including but not limited to industry standard connectivity, reporting tools, OLAP tools, and backup and recovery standards.[citation needed] Additionally, object databases lack a formal mathematical foundation, unlike the relational model, and this in turn leads to weaknesses in their query support. However, this objection is offset by the fact that some ODBMSs fully support SQL in addition to navigational access, e.g. Objectivity/SQL++, Matisse, and InterSystems CACHÉ. Effective use may require compromises to keep both paradigms in sync.

In fact there is an intrinsic tension between the notion of encapsulation, which hides data and makes it available only through a published set of interface methods, and the assumption underlying much database technology, which is that data should be accessible to queries based on data content rather than predefined access paths. Database-centric thinking tends to view the world through a declarative and attribute-driven viewpoint, while OOP tends to view the world through a behavioral viewpoint, maintaining entity-identity independently of changing attributes. This is one of the many impedance mismatch issues surrounding OOP and databases.

Although some commentators have written off object database technology as a failure, the essential arguments in its favor remain valid, and attempts to integrate database functionality more closely into object programming languages continue in both the research and the industrial communities.[citation needed]

[edit] See also

[edit] References

  1. ^ Data Integration Glossary, U.S. Department of Transportation, August 2001.
  2. ^ Kim, Won. Introduction to Object-Oriented Databases. The MIT Press, 1990. ISBN 0-262-11124-1
  3. ^ Bancilhon, Francois; Delobel,Claude; and Kanellakis, Paris. Building an Object-Oriented Database System: The Story of O2. Morgan Kaufmann Publishers, 1992. ISBN 1-55860-169-4.
  4. ^ "Lessons Learned From Managing A Petabyte"
  5. ^ Barry, Douglas and Duhl, Joshua. Object Storage Fact Books: Object DBMSs and Object-Relational Mapping. Barry & Associates, Inc., 2001. Pages showing the ODMG compliance for both object database and object-relational mapping products in 2001.
  6. ^ Animation showing how an object database works

[edit] External links

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