ISO 20217-2015 pdf free

09-03-2021 comment

ISO 20217-2015 pdf free.Space data and information transfer systems一Spacecraft onboard interface services一File and packet store services.
2.2 FILE STORE OVERVIEW
2.2.1 TYPES OF FILE STORES
A tile store is considered to be a tile system and the associated sorage medium.
At the highest level a file system is a way to organize, store, retrieve, and manage information on a permanent storage medium. File stores manage permanent storage and form an integral part most onboard spacecraft data handling systems.
Different types of file systems (and file stores) may be considered:
a) Flat file systems. Designed to not have subdirectories. Everything is stored in (he root level of the storage media.
b) Hierarchical tile systems. Designed to organize information in directories in a tree- like structure.
Either of these may be used to support the FPSS services and no restriction is imposed on the type of file store. This approach allows complete independence from the technology used to implement the file store. The way in which this mapping is performed is implementation- specific.
The FPSS allow for multiple client processes on multiple machines for both accessing and updating tiles. Hence updates to the file from one client should not interfere with access and updates from other clients. It is assumed that concurrency control or locking is handled by the file store itself. In support of this, file locking functionality is provided. An application (the ‘lock owner’) may lock a file to various degrees of access (exclusive read-only, read- only by all, exclusive access) from other user entities. Any user entity may unlock the file.
NOTE — It is implementation-specific if unlocking of files is restricted to. for example, a ‘super-user’ application.
2.2.2 CURRENT I)IRECTORY
The current directory within a file store for each application is maintained by the file system. A number of operations are performed relative to an application’s current directory, e.g., creating a file. By default, upon initialization, the application’s current directory is a the root level of the storage niedia for flat file systems and at the root level of the tree for hierarchical file systems. For hierarchical file systems, each application’s current directory can be changed by request.
2.2.3 TYPES OF FILES
A file is where a user stores information. Files are logically organized into one-dimensional arrays of octets. The format of a file is defined by its content since a file is solely a container for data. The size of data stored is arbitrary and may range from only a few octets to the entire capacity of the entire mass memory in which files reside. Files are not limited in size (subject to the limitations of the mass memory in which the files reside). A file store should be able to hold a potentially large number of files, where ‘large’ ranges from tens of thousands to millions.ISO 20217 pdf download.

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