| Abstract |
TELOS is an object oriented language for knowledge representation which provides effiecient mechanismhs to describe semantic networks. It is used within the ITHACA project for the description of software components that are stored in a Software Information Base (SIB). Software engineers browse through the contents of the SIB and select software components for reuse or already existing components. The purpose of this thesis is the design and implementation of the various structures that are used for storing the contents of the SIB. These structures are integratedwith appropriate mechanisms that provide TELOS applications with an interface to access, insert or update the contents of the SIB, forming a kernel through which all operations in the SIB are performed. Each object is identified by a unique object identifier which is assigned to the object by the system catalogoue mechanism. This mechanism implements every access to the SIB for each and on disk. The system catalogue is essentially an access mechanism where objects are accessed through use of their unique object identifiers. The access methods are efficient, allowing the system to exhibit competitve performance in typical applications. Objects on disk and in memory are represented by identical data structures, avoiding thus the computational cost for tranforming them from one format to another when they are exchanged between memory and disk. Objects are organized on disk in object blocks, whose size is equal to the disk block size. Objects are read/stored from.on files in disk block basis. Objects residing in the same block belong to the same object type. When an object is read fro disk, the whole object where the block resides, is fetched in memory, therefore all other objects residing in the same object block are prefetched. The SIB users identify objects by means of logical names while the runtime system uses the object identifiers for every operation performed on objects. Logical name translation to the corresponding object identifier and vice versa is performed by the symbol table. This table exploits access mechanisms that facilitate efficient translation between logical names and object identifiers. The storage structures for the object blocks, the system catalogue and the symbol table in memory, reside in corresponding caches. The cache mechanisms enable immediate system start-up regardless of the SIB size and enhance system performance which compares to that of commercial object oriented data base systems.
|
Ο Μηχανισμός Αποθήκευσης και Διαχείρισης Οντοτήτων για τη Γλώσσα Παράστασης Γνώσης TELOS
