Chapter 6 

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6.5.3 Metadata

Metadata is information that describes the characteristics of a data set. For an EIS

system, metadata describes the content, quality, and condition (among other charac 

teristics) of the EIS's data. 

EISs provide a range of access to this metadata. Some EISs provide program 

matic access to their metadata, while others provide the metadata information in

text form only, as a form of documentation. Sometimes, the metadata information

is available through database system support tools. For example, some databases

allow queries to learn its table names and schemas. Similarly, an EIS may give

you access to its various quality of service parameters.

Metadata is often relevant to integration. Metadata allows you to use tools to

discover properties of enterprise systems, and from this discovery to create appro 

priate, easy to use facades to the systems. By having access to metadata, tools can

generate more meaningful classes. 

Web services are designed to support metadata. Web services rely on WSDL

files, which essentially provide metadata describing the services, the operations

offered by the services, parameters for these operations, and so forth. Since these

WSDL files are XML documents, they are accessible to tools and other programs.

(See  Web Services Description Language  on page 36.)

Using an integration layer helps make metadata more explicit. When metadata

is implicitly associated with EIS data, tools may have a difficult time discovering

the metadata. For example, a database table column may represent distances from

a certain point, and these distances are implicitly measured in miles. A tool that

accesses the data from this table column may not be able to determine whether the

distance is measured in miles or kilometers. By creating an integration layer, you

can make this information explicit. You can name the methods that access the data

in such a way as to indicate the associated metadata. For example, rather than

have a 

getDistance

 method, you can call the method 

getDistanceInMiles

. For

Web services, the standard document formats that describe the service are

designed to make the metadata more explicit.

Another way to make metadata explicit and accessible, especially for medium

to large enterprises, is to store the metadata in a central location, such as a tradi 

tional LDAP directory. (LDAP, which stands for Lightweight Directory Access

Protocol, is an Internet protocol that programs can use to look up information

from a server.) You can make your EIS's metadata available to others in several

ways. You can enable metadata support in your enterprise systems. The WSDL

file that accompanies a Web service already defines metadata for the service. You