Information Systems Reengineering, Integration and Normalization - Information Systems Reengineering, Integration and Normalization - page 20

unique key transformation. The complication in semantic analysis appears not only
in the DDL of the schema, but also in the database programs. The automation of the
direct translation from procedural (with database navigation) nonrelational DML
statement to nonprocedural (without database navigation) relational DML statement
is still a challenge to database researchers.
To resolve the above mentioned problems, an alternative approach for database
reengineering is endorsed in a methodology of RELIKEDB (Relational-like-da-
tabase; Fong 1993 ), which is similar to the relational interface approach in that
both provide a relational interface to make the hierarchical or network DBMS a
relational-like DBMS.
RELIKEDB provides schema translation in which user input contributes to the
process. Direct schema translation from a hierarchical model or network model into
a relational cannot guarantee the capture of all the original conceptual schema se-
mantics. With user input, we can at least provide a relational schema that is closer to
the user's expectations, and which preserves the existing schema's constraints such
as record key, relationships, and attributes.
As to data conversion, RELIKEDB provides algorithms to unload a hierarchical
or a network database into sequential files directly and efficiently, which can then
be uploaded into a relational database.
In program translation, RELIKEDB provides an “open” data structure by adding
secondary indices in the existing hierarchical or network database. This eliminates
the navigation access path required to retrieve a target record from a system record.
Instead, each target record type can be accessed directly without database naviga-
tion. The database access time is thus reduced and the program conversion effort
is simplified. RELIKEDB provides algorithms to translate SQL statements into hi-
erarchical or network DML statements. These are sound solutions to the program
conversion problem.
Chapter 6 describes in detail the proposed three-phased methodology of
RELIKEDB to add a relational interface atop of nonrelational database.
As to the program translation from a relational to object-oriented form, the dif-
ficulty is that there is no standard object-oriented database DML at present.
As XML becomes data standard on the Internet, there is a need for a company in-
teroperating its relational database and XML database together for its applications.
For example, a company can use relational database for production application, and
XML database for e-commerce on the Internet at the same time.

1.4.3 Schemas Integration

Chapter 7 descibes schemas integration of heterogeneous databases including rela-
tional schemas, object-oriented schemas, and XML schemas. The integration is to
locate the relevance of the schemas such as their data semantic relevance of cardi-
nality, isa, generalization, and categorization, etc.