Metadata
Files associated with metadata:
Name: metadata.xml
Document Type Definition: metadata.dtd
Purpose
This validated XML file provides the status of the corresponding frame store. It contains the status of and the metadata associated with each buffer in the corresponding data directory. The validation is done using the appropriate Document Type Definition (DTD) file, located in the same directory.
Attributes
The metadata XML file is readable and writable. The DTD file is always read-only.
Metadata Queue
Each time a buffer is filled with new data from the board, the driver provides associated metadata. This data is stored by the Virtual File System driver in a queue. The queue always holds as many items as buffers and corresponding files in the data directory.
The application tells the driver when a buffer (a data file) may be disposed of and eventually overwritten by new data. This modifies items in the queue.
Read
When the application opens the XML file, the driver generates its content from the information of the driver-maintained queue. This ensures that reading the file, even partially, always produces valid data.
Reading the whole file provides the listing of all metadata from queue.
Write
The file can be written, to selectively edit metadata.
The only useful action is to add the Dispose element to a MetaData element. The corresponding buffer and data files are disposed of as soon as the XML block corresponding to that metadata is completely parsed. If a parsing error occurs, the metadata causing the error and the subsequent ones are ignored.
The only XML elements required to dispose a buffer are Index and Dispose. All other elements are allowed but ignored.
Delete
Deleting a metadata file is allowed, at any time. It flushes the metadata queue and marks all buffers unlocked. A new file reappears immediately thereafter, with updated content.
Synchronization
Several applications can access the files simultaneously. When doing so, it is the application's responsibility to synchronize the file accesses.