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File Processing : Other Issues

File Processing : Other Issues. 2007, Spring Pusan National University Ki-Joune Li. Data Dictionary : What does it contain ?. Data dictionary (also called system catalog ) stores M etadata Information about relations names of relations names and types of attributes of each relation

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File Processing : Other Issues

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  1. File Processing : Other Issues 2007, Spring Pusan National University Ki-Joune Li

  2. Data Dictionary : What does it contain ? • Data dictionary (also called system catalog) stores Metadata • Information about relations • names of relations • names and types of attributes of each relation • names and definitions of views • User and accounting information, including passwords • Statistical and descriptive data • number of tuples in each relation • Physical file organization information • How relation is stored (sequential/hash/…) • Physical location of relation • operating system file name or • disk addresses of blocks containing records of the relation • Information about indices

  3. Relation-metadata (relation-name, number-of-attributes, storage-organization, location)Attribute-metadata (attribute-name, relation-name, domain-type, position, length) User-metadata (user-name, encrypted-password, group) Index-metadata (index-name, relation-name, index-type, index-attributes) View-metadata (view-name, definition) Data Dictionary : How to Represent it • Data structure • specialized data structures designed for efficient access • a set of relations, with existing system features used to ensure efficient access • The latter alternative is usually preferred

  4. Persistent Object • Objects in C++ program • Volatile Object : Disappears with the termination of program • Persistent Object • Non-Volatile Object : Keeps its status despite of its termination • A Necessary Condition for Object-Oriented Databases • Object vs. Record

  5. OID : Object Identifier • ID given by system • the only way to identify object • one ID per an object • Logical OID vs. Physical OID • Logical OID • No direct specification from OID to physical location • Need an index that maps an OID to the object’s actual location. • Physical OID • encodes physical location of the object • Physical OIDs typically have the following parts: • a volume or file identifier • a page identifier within the volume or file • an offset within the page

  6. Pointer OID Pointer Swizzling Pointer Swizzling Object Object Main Memory Disk Space

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