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UMD CMSC 424 - Database Design Goals, Normalization, Normal Forms

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Recap of Feb 20: Database Design Goals, Normalization, Normal FormsGetting Physical: Storage and File Structure (Chapter 11)Chapter 11Midterm!Midterm Study and Homework #2Classification of Physical Storage MediaPhysical Storage Media Overview (11.1)Physical Storage Media -- Cache and Main MemoryPhysical Storage Media -- Flash MemoryPhysical Storage Media -- Magnetic DiskPhysical Storage Media -- Optical StoragePhysical Storage Media -- Tape StorageStorage HierarchyMagnetic Disks (11.2)Magnetic Disks (cont)Slide 16Slide 17Disk Performance MeasuresDisk Performance Measures (cont.)Optimization of Disk-Block Access: MotivationOptimization of Disk-Block Access: MethodsSlide 22Slide 23Slide 24Storage Access (11.5)Buffer ManagementBuffer Replacement StrategiesSlide 28Buffer Management (cont)Slide 30Recap of Feb 20: Database Design Goals, Normalization, Normal Forms•Goals for designing a database: a schema with:–simple, easy to phrase queries–avoids redundancies (repetition of information)–avoids anomalies –good performance•Normalization–decompose complex relations–Lossy decompositions–Functional Dependencies•Normal Forms: 1NF, 2NF, 3NF, BCNF–BCNF or 3NF: lossless decomposition in both•BCNF can’t always ensure dependency preservation•3NF sometimes requires null values or redundant informationGetting Physical: Storage and File Structure (Chapter 11)•Up until now we have examined database design from a high-level conceptual view, passing over actual implementation and underlying hardware.–Appropriate focus for database users–But hardware does have an influence on implementation, and implementation does have an influence on what conceptual designs will be more efficient and useful•Now we get physical -- examine physical storage media to give a background for later focus on implementation of the data models and languages already describedChapter 11At this point we are focussing on the following sections•11.1 Overview of Physical Storage Media•11.2 Magnetic Disks•11.3 RAID (very briefly)•11.4 Tertiary Storage•11.5 Storage Access•11.6 File Organization•11.7 Organization of Records in Files•11.8 Data-Dictionary StorageMidterm!•As per the syllabus, the Midterm will cover the pre-midterm lecture notes plus sections 1,2,3 (except 3.4 & 3.5), 4, 6, 7-7.7, 11 (except 11.3 and 11.9) of the text•We have examined all that material except chapter 11, which starts today•Scheduling the midterm depends upon the speed with which we get through the material.•It looks as if we’ll have enough time to schedule one day for review before the midterm•My current guess is that we might be able to schedule the midterm as early as March 13; certainly no later than March 20. I’m aiming for Tuesday, March 18.Midterm Study and Homework #2•Material you are responsible for:–All material presented in class before the midterm–Textbook sections 1,2,3 (except 3.4 & 3.5), 4, 6, 7-7.7, 11 (except 11.3 and 11.9) •The homework questions from assignment 1 (exercises 1.1, 1.2, 1.3, and 2.1-2.6) are all useful study aids, as are the questions from homework assignment #2:–3.2, 3.3, 3.5, 3.6 -- 3.9, 3.16–4.1, 4.2, 4.4 -- 4.8–7.2, 7.4, 7.5, 7.11, 7.12, 7.15, 7.16, 7.21, 7.23•Homework #2 is due Tuesday, March 11. I’ll try to have them back to you, graded, Thursday March 13 so you can use them as a study aid for the exam Tuesday, March 18.Classification of Physical Storage Media•Media are classified according to three characteristics:–speed of access–cost per unit of data–reliability•data loss on power failure or system crash•physical failure of the storage device•We can also differentiate storage as either–volatile storage–non-volative storagePhysical Storage Media Overview (11.1)•Typical media available are:–Cache–Main memory–Flash memory–Mag disk–Optical storage (CD or DVD)–Tape storagePhysical Storage Media -- Cache and Main Memory•Cache–fastest and most costly form of storage–volatile–managed by computer system hardware•Main memory–fast access (10s to 100s of nanoseconds)–generally too small or expensive to hold the entire database•current capacities commonly used are up to a few Gigabites •capacities have gone up and per-byte costs have decreased steadily, roughly a factor of 2 every 2-3 years–volatilePhysical Storage Media -- Flash Memory•Also known as EEPROM -- Electrically Erasable Programmable Read-Only Memory•non-volatile•reading data is comparable to main memory speeds•writing is more complex–can’t overwrite a single location -- a whole bank of memory must be erased to permit writing within that bank.–erasing is only supported a limited number of times -- 10,000 to one million erase cycles–writes are slow (a few microseconds), and erases are slower•cost comparable to main memory•widely used in computer systems embedded in other devices, such as digital cameras and hand-held computersPhysical Storage Media -- Magnetic Disk•data is stored on a spinning disk and read/written magnetically•primary medium for long-term storage of data•typically stores entire database•data must be moved from disk to main memory for access, and written back for storage–much slower access than main memory (about which more later)•direct access -- possible to read data on disk in any order, unlike magnetic tape•capacities up to 100 gig–much larger capacity and cheaper cost/byte than main memory or flash memory–capacity doubles every two or three years•survives power failures and system crashes–disk failure can destroy data, but this is more rare than system crashesPhysical Storage Media -- Optical Storage•Non-volatile; data is read optically from a spinning disk using a laser•CD-ROM (640 MB) and DVD (4.7 to 17 GB) most popular forms•Write-once, Read-many (WORM) optical disks used for archival storage (CD-R and DCD-R)•Multiple-write versions also available (CD-RW, DVD-RW, and DVD-RAM)•Reads and writes are slower than with magnetic disk•Juke-box systems available for storing large volumes of data–large numbers of removable disks–several drives–mechanism for automatic loading/unloading of disksPhysical Storage Media -- Tape Storage•Non-volatile•used primarily for backup (to recover from disk failure) and for archival data•sequential access -- much slower than disk•very high capacity (40-300 GB tapes available)•tape can be removed from drive; storage


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UMD CMSC 424 - Database Design Goals, Normalization, Normal Forms

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