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Graphic Tools for Legacy Database Migration


Status

Advanced

Purpose and Origin

Graphic tools for legacy database migration are used to aid in the examination of legacy data in preparation for migration of one or more databases, often as part of a system migration or reengineering effort. They are intended to enhance understandability and portability of databases by providing easily-manipulated views of both content and structure that facilitate analysis [Selfridge 94].

Technical Detail

A graphical tool portrays a database's organization and data in graphical form. This enhances the understandability of the database(s) by allowing the analyst to assess the condition and organization of the data, including overlap and duplication of data items, in preparation for migration. This enhancement is desirable for several reasons:

  1. Databases are typically complex, and may lack adequate documentation.
  2. The information to be migrated may be contained in several separate databases built for different purposes.
The latter usually creates data redundancy, including multiple instances of a field, and even different representations of the same data (e.g., floating point in one place, fixed point or text in another). Important legacy information may be buried in text fields that must be found in order to capture the data's content. Bennett describes some of these problems [Bennett 95]. Legacy database migration is usually done to improve a system's maintainability (modifiability, testability, and/or ease of life cycle evolution). Database migration is typically performed as part of a larger system reengineering effort. It is a branch of database design and engineering, and requires the same set of disciplines.

Usage Considerations

A visualization tool is only part of the toolset of interest in migrating legacy data. Other tools might include the following:

  • data modelers
  • data entry and/or query screen translators
  • report translators
  • data-moving and translation utilities
A migration strategy is required to create a normalized file structure with referential integrity out of large, multiple databases. The tools must fit the environment, and the target database must be interfaced with the system and application software; this implies the need for compatibility with the languages used. The design of the target database can greatly affect performance and maintainability; therefore the first goal of the migration effort should be to define a target schema suitable for the application.

Maturity

Major database vendors offer tools of this type; the tools are typically optimized toward their database product as the target, but they accept other databases as input. There are also independent sources of visualization tools, as well as tools produced by research efforts [Selfridge 94, Gray 94]. Database migration, when offered as a service, often uses visualization tools to facilitate understanding between customer and consultant about the migration approach, process, and results [Ning 94].

Costs and Limitations

The cost of such a tool, including training, should be nominal compared to the total cost of the target database system's software, and may even be included. However, the migration itself can be costly in time and training; experience is required for good, normalized database design.

Dependencies

A migration effort would typically be coincident with a reengineering of the software that access the data, and would be intimately tied to the approaches used to do this reengineering.

Alternatives

An alternative to migration of the database is to link existing heterogeneous databases to each other. This approach eliminates the need to migrate the data, but also retains all the structural inefficiencies of the current databases, and may degrade performance. It may also create maintainability problems because each old database will require a separate knowledge set, and because their platforms may be not be supportable. The approach requires writing interface software that act as gateways to the other database management systems (DBMS), file systems, and/or other existing applications. The Object Request Broker technology exemplified by the emerging Common Object Request Broker Architecture (CORBA) standard, as well as products offered by commercial database vendors, offer the capability to link existing heterogeneous databases. This includes the ability to associate data elements in different databases, and do JOINS across database boundaries.

Complementary Technologies

Other tools for analyzing data content and structure are available from commercial vendors and academic and research organizations. Knowledge-based approaches, for example, may have the ability to infer identity between multiple, differently-named instances of a data item. Other approaches such as these can compliment the use of graphical analyzers. Migration is typically done in the context of open systems (see COTS and Open Systems--An Overview), which implies a large number of technologies that would be helpful together.

Index Categories

This technology is classified under the following categories. Select a category for a list of related topics.

Name of technology

 Graphic Tools for Legacy Database Migration

Application category

 Database Design (AP.1.3.2)
Reengineering (AP.1.9.5)

Quality measures category

 Understandability (QM.3.2)
Maintainability (QM.3.1)
Testability (QM.1.4.1)
Compatibility (QM.4.1.1)
Throughput (QM.2.2.3)

Computing reviews category

 Database Management - Logical Design (H.2.1)

References and Information Sources

[Bennett 95] Bennett, K. "Legacy Systems: Coping With Stress." IEEE Software 12, 1 (January 1995): 19-23.
[Gray 94] Gray, W. A.; Wikramanayake, G. N.; & Fiddian, N. J. "Assisting Legacy Database Migration," 5/1-3. IEE Colloquium: Legacy Information System- Barriers to Business Process Re-Engineering (1994/246). London, UK, December 13, 1994. London, UK: IEE, 1994.
[Ning 94] Ning, Jim Q.; Engberts, Andre; & Kozaczynski, W. "Automated Support for Legacy Code Understanding." Communications of the ACM 37, 5 (May 1994): 50-57.
[Selfridge 94] Selfridge, Peter G. & Heineman, George T. "Graphical Support for Code-Level Software Understanding," 114-24. Ninth Knowledge-Based Software Engineering Conference. Monterey, CA, September 1994. Los Alamitos, CA: IEEE Computer Society Press, 1994.

Current Author/Maintainer

Edmond VanDoren, Kaman Sciences, Colorado Springs

Modifications

10 Jan 97 (original)
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URL: http://www.sei.cmu.edu/str/descriptions/gtldm_body.html
Last Modified: 11 January 2007