The data from different sources available in heterogeneous format calls for modularity in the metadata description. The users can make use of the existing schemas rather than defining something new from the scratch.
The support for interoperability allows the data from different schemas for the seamless syntax and semantic integration. This helps in re usability of the module in different applications.
HTML based metadata is popularly associated with the content and services associated with the web. Although it is simple, it fails to provide the description in a structured fashion.
It supports the structured data although used in a small scale. Like XML, it is modular and extensible and Interoperable.