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CASSIS Interoperability - Metadata
Coordination Action for the integration of

Solar System Infrastructures and Science

Structural Metadata

Structural Metadata describes the actions that can be performed on data and metadata elements. It also allows the use of software repositories and processing services to perform actions on data in a well-defined manner. In essence it is the verbs to other metadata's nouns.

The structural metadata should be designed with change in mind. During the lifetime of a large project there will probably be a number of changes in technology and the way that systems interact and the design of the system metadata should not preclude being able to benefit from these changes. It therefore needs to be modular and layered, with all required information being contained in files that can easily be extended and modified.

It is also important that the design should be try to be agnostic of the domain as far as possible – this will facilitate interoperability.

File Naming and Storage

Assuming that the data can be made easier to use across domain boundaries by improving the quality of the Observational Metadata, the next task is to make them more accessible. Following a few simple rules in the way files are named and in the directory structure used to hold them can make a significant difference to how easily they can be accessed.

There are no hard and fast rules for file names, but the names should be sufficiently unique that files can be stored outside of their "native environment" – i.e. where they are normally stored on the system of the group that generated the file. In other words, the file should be able to exist without causing confusion when removed from the context of where it is normally stored.

The file names should also ideally identify the type and origin of the file, the nature of the data and when the observations were made; the name might also indicate if an image represented a partial or the full field-of-view of the instrument.

Although not strictly metadata in itself, the structure of the archive can make a lot of difference to how easily the data can be accessed. If the data are held in a hierarchical structure based on date and time, it is much simpler to create metadata that can be used to find the required data. Storage with this type of structure is essential for resource-poor providers and would be beneficial for data centres.

A summary of observations that have been made, or Observational Catalogue, is useful and simplifies access. It is particularly useful if not all the observations in the archive are available on-line.

Service Interfaces

Many of the components in research infrastructures are in the form of services. These are stand-alone capabilities that are ideally Web Service interfaces that conform to a standard model.