19.1.1.5 Important Usage of these Technologies for DAS

• DAS data objects use the following XSDs:

• The optical path is represented using the PRODML Fiber Optical Path, which is shared with the DTS (Distributed Temperature Sensing) schemas (see 14.3 Defining the Optical Path ).

• All other DAS concepts use schemas developed specifically for DAS.

• Metadata. All of the metadata about the DAS Acquisition—but not the arrays of data—are stored in XML files. The metadata also is stored in the HDF5 files, along with the arrays of numbers. The advantages of having this data in the XML include:

• XML has built-in schema validation, and all Energistics XML standards work on the basis that the standard is represented by XSD schemas. HDF5 does not include schema-based validation. This means that the DAS XML files can be checked for validity by simple schema validation built in to most XML tools and editors.

• The XML files are small and can be opened in any editor, including a text editor, which may make it much easier to figure out what the content of the set of acquisition files is, compared to opening all the potentially huge HDF5 array files. All the metadata can sit in one small XML file, while the actual measurement values are in many large HDF5 files.

The HDF5 files also contain the metadata. The metadata is duplicated from the XML files because it is possible that the HDF5 files— which can easily fill several hard drives with raw data—may become physically separated from the small XML file during transit. Having the metadata in each HDF5 file enables files to be assembled back together as a coherent set.

For more information about HDF5 configuration options for DAS, see 19.5.3 HDF5 File Array Configuration Options .

• EPC. The EPC Specification states that HDF5 files may be stored either inside or outside of the EPC file; however, DAS requires that HDF5 files be stored outside the EPC file.

• Relationships between data object. The XML content is also used to provide the links between the metadata and the data arrays, through Energistics data object reference, which gets implemented in the EPC file.