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Databasesystemer

Databasesystemer. Data Structure, Storage and Processing Architectures. Learning objectives. Be able to explain what a database architecture is and what goals the design strives to achieve. Know different data storage structures and storage devices, and when to use them. Goals.

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Databasesystemer

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  1. Databasesystemer Data Structure, Storage and Processing Architectures Data Structure and storage Object-oriented Data Management

  2. Learning objectives • Be able to explain what a database architecture is and what goals the design strives to achieve. • Know different data storage structures and storage devices, and when to use them. Data Structure and storage Object-oriented Data Management

  3. Goals • An architecture should • Respond to queries in a timely manner • Minimize the cost of processing data • Minimize the cost of storing data • Minimize the cost of data delivery • These objectives can be conflicting Data Structure and storage Object-oriented Data Management

  4. Database access Data Structure and storage Object-oriented Data Management

  5. A disk Disk head Disk arm Rotation Arm movement Tracks, bloks and sectors Cylinder Data Structure and storage Object-oriented Data Management

  6. Clustering • Records that are often retrieved together should be stored together • Intra-file clustering • Inter-file clustering Data Structure and storage Object-oriented Data Management

  7. Sequential retrieval • Consider a file of 10,000 records each occupying 1 page • Queries that require processing all records will require 10,000 accesses • e.g., Find all items of type 'E' • Many disk accesses are wasted if few records meet the condition Data Structure and storage Object-oriented Data Management

  8. Indexing Data Structure and storage Object-oriented Data Management

  9. Multiple indexes Data Structure and storage Object-oriented Data Management

  10. Sparse indexes Data Structure and storage Object-oriented Data Management

  11. B-tree (B+ tree) • Sequence set is a single level index with pointers to records • Index set is a tree-structured index to the sequence set Data Structure and storage Object-oriented Data Management

  12. Hashing hash address = remainder after dividing SSN by 10000 S S N D i s k a d d r e s s F i l e s p a c e O v e r f l o w a r e a 4 1 7 - 0 3 - 4 3 5 6 } 4 3 5 6 4 1 7 - 0 3 - 4 3 5 6 5 3 2 - 6 7 - 4 3 5 6 5 3 2 - 6 7 - 4 3 5 6 8 9 1 - 5 5 - 4 3 5 6 • • S y n o n y m c h a i n } 0 4 3 - 1 5 - 1 8 9 3 1 8 9 3 0 4 3 - 1 5 - 1 8 9 3 8 9 1 - 5 5 - 4 3 5 6 • • } 2 8 1 - 2 7 - 1 5 0 2 1 5 0 2 2 8 1 - 2 7 - 1 5 0 2 • Data Structure and storage Object-oriented Data Management

  13. Linked list Data Structure and storage Object-oriented Data Management

  14. Join indexes Data Structure and storage Object-oriented Data Management

  15. A D C B E Y X X Y I n d e x s e t A B D E S e q u e n c e s e t C R-trees Data Structure and storage Object-oriented Data Management

  16. A D C B E Y X R-tree searching Data Structure and storage Object-oriented Data Management

  17. Fysisk design og tuning • Hvad er databasens arbejdsbelastning? • Hvilke index skal oprettes? • Skal der ske tilpasning i de ”conceptual schema” af performance hensyn? Data Structure and storage Object-oriented Data Management

  18. Guidelines for valg af index • Hvornår der oprettes et index? • Valg af en søge nøgle for indexet. • Hvornår anvendes ”multiple-attribute” søge nøgle? • Hvornår skal der foretages ”clustering”? • Valget mellem ”hash” og B+ tree. • Index – omkostning for vedligeholdelse. Data Structure and storage Object-oriented Data Management

  19. Data storage devices • What data storage device will be used for • On-line data • Access speed • Capacity • Back-up files • Security against data loss • Archival data • Long-term storage Data Structure and storage Object-oriented Data Management

  20. On-line Data Storage • Harddisk • RAID • “Mirroing” • “Stripping” Data Structure and storage Object-oriented Data Management

  21. Mirroring Data Structure and storage Object-oriented Data Management

  22. Striping Data Structure and storage Object-oriented Data Management

  23. Storage life Magnetic tape Half-inch reel-to-reel Half-inch tape cartridge VHS tape Quarter-inch tape Optical disk CD-ROM (read only) CD-R (recordable) Microfilm Medium-term film Archival quality (silver) Paper Newspaper High quality Permanent 1 10 100 500 Storage life in years of high quality brands Data Structure and storage Object-oriented Data Management

  24. Databasesystemer Object-oriented Data Management Data Structure and storage Object-oriented Data Management

  25. Learning objectives • Explain the main concepts of object-orientation. • Mapping a simple object-oriented model to a relational model. Data Structure and storage Object-oriented Data Management

  26. Data and OO modeling Data Structure and storage Object-oriented Data Management

  27. Key concepts • Object instances and classes • Encapsulation • Message passing • Generalization/specialization hierarchies • Inheritance Data Structure and storage Object-oriented Data Management

  28. Object instances and classes • Object instance • Single representations • Object classes • A collection of objects of the same type • e.g., SHARE • Similar concept to an entity • Object identification (OID) • Unique reference to an object instance Data Structure and storage Object-oriented Data Management

  29. Encapsulation • A central concept • All the processing is done within the object • An object is shielded from interference by other objects Data Structure and storage Object-oriented Data Management

  30. Message passing • Objects communicate by sending and receiving messages • The receiving object needs a method for handling the message • A message can trigger a change in a receiving object Data Structure and storage Object-oriented Data Management

  31. Generalization/specialization hierarchies • Classes can be generalizations or specializations of other classes • ACADEMIC PERSON is a generalization of subclasses student and staff • STUDENT is a specialization of superclass ACADEMIC PERSON Data Structure and storage Object-oriented Data Management

  32. Inheritance • A subclass can inherit the data and methods of its superclass • Simplifies programming • Creates reusable objects Data Structure and storage Object-oriented Data Management

  33. Layers of an OO model • Class and object layer • Structure layer • Attribute layer • Service layer Data Structure and storage Object-oriented Data Management

  34. Object layer • Identifying objects and classes • Underline the nouns in the problem description Customers can rent diving equipment and boats from DDT. When a customer has seen what is available and decided what to rent, a rental agreement or contract is produced and signed Data Structure and storage Object-oriented Data Management

  35. Structure layer • Generalization/specialization • Whole/part Data Structure and storage Object-oriented Data Management

  36. Object model – take 1 Data Structure and storage Object-oriented Data Management

  37. Attribute layer • Specification of attributes • Specification of association relationships • Specification is similar to data modeling Data Structure and storage Object-oriented Data Management

  38. Object model - final version Data Structure and storage Object-oriented Data Management

  39. Service layer • Describes processing for each specified object • Simple services • Standard services all objects are expected to perform • Implicit and not shown • Complex • Non-standard services • Shown explicitly Data Structure and storage Object-oriented Data Management

  40. Class Diagram to ER Diagram • To Convert... • Each class becomes an entity • Class attributes become entity attributes • Type information is maintained • Operation information is ignored • Each association becomes a relationship • Multiplicity information is maintained • IsA Relationship should become an IsA (super/sub) relationships • SA does not do this translation • Overcome be manually adding an entity equivalent to the class and then created a relationship of type super/sub Data Structure and storage Object-oriented Data Management

  41. ER Diagram to Database Tables • Use entity names for table names • Select a primary key for each entity/table • Post all attributes of an entity as column names in the entity’s table • For 1:1 cardinality relationships • All attributes can be merged into a single table • For 1:N cardinality relationships • Post the identifier from the “one” side as an attribute to the “many” side • For N:M cardinality relationships • Create a new table and post the primarykeys from each entity as attributes in the new table Data Structure and storage Object-oriented Data Management

  42. Mapping attributes • Each attribute is mapped to zero or more columns • Non-persistent (i.e., derived) attributes are not mapped • Some attributes need to be broken into components Data Structure and storage Object-oriented Data Management

  43. MappingGeneralization • Vertical • Each class is mapped to a separate table • Recommended • Horizontal • Each subclass is mapped to a different table • The superclass is not mapped to a table • Filtered • All classes are mapped to the same table • The table contains columns for all attributes in both classes with a column added to distinguish between the subclasses. Data Structure and storage Object-oriented Data Management

  44. MappingAssociation and aggregation • Associations are mapped like their corresponding data model parallels • e.g., a m:m association is mapped by creating an associative entity • Physically, an aggregation might be implemented using clustering or a linked list because the whole and parts are often retrieved together Data Structure and storage Object-oriented Data Management

  45. Class Exercise • Convert the following class diagram to • ER diagram Data Structure and storage Object-oriented Data Management

  46. OO and relational paradigms Data Structure and storage Object-oriented Data Management

  47. The role of the ODBMS • Objects have a life that extends beyond the execution of the OO program • Persistent objects live longer than the methods that create them • An ODBMS stores data when the OO application is not running Data Structure and storage Object-oriented Data Management

  48. Features of an ODBMS • An ODBMS should supports OO concepts • complex objects • abstract data types • encapsulation • inheritance • An ODBMS also should provides • data sharing • concurrent data access • recovery control Data Structure and storage Object-oriented Data Management

  49. The Object Database Standard • The OMG (Object Management Group) is creating and promulgating a standard for OO technology • The goal is to minimize incompatibility across platforms and standardize some features • OMG has released an Object Database Standard Data Structure and storage Object-oriented Data Management

  50. ODBMS versus RDBMS • Support for storage and manipulation of complex objects • Raised the level of abstraction by introducing classes and inheritance • Overcomes the impedance mismatch • Set level processing with SQL makes ad hoc querying easier than record-at-a-time processing Data Structure and storage Object-oriented Data Management

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