public management: concepts and big...

Data Structure & File Structure

Hun Myoung Park, Ph.D.,Public Management and Policy Analysis Program

Graduate School of International RelationsInternational University of Japan

OutlineData TypeData StructureFile StructureFile SystemDirectoryBinary versus Text Files

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Data TypeAbstract data types (ADT) include

Stack (LIFO) Queue (FIFO) List, tree and graph

Primitive type: number, string, booleanComposite type (bundling of elements):

array and record

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Data StructureA way of storing and organizing data. “A collection of related variables that can be

accessed individually or as a whole”“A set of data items that share a specific

relationship”Implements abstract data typesArrays, records, and linked lists.Array (fixed-size sequence of elements) vs. list

(variable size)

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Data Structure: ArrayA sequenced collection of elements Elements may or may not share the same

data type Array name, or array name and index

(subscript) to refer to elements. a[0], a[1], a[2]… instead of a0, a1, a2, …Array name alone a means a[0], a[1],…Multi-dimensional array a[0][3]

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Data Structure: RecordA collection of related elements (fields or

attributes) of an entityThe name of a record is the whole structure

name (e.g., student)The names of fields (e.g., name, id,…)student.name, student.id, student.age, …Array of records (e.g., student[1].name,

student[1].id, … student[2].name, student[2].id, …)

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Data Structure: Linked List“A collection of data in which each element

contains the location of the next element.”Consists of data and linkData contain information to be processedLink contains a pointer (address) that

identifies the next element in the list. The last element contains data only (null

pointer)

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Array versus Linked List

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File Structure“An external collection of related data

treated as a unit”Used to store data permanently in a

secondary storage device or auxiliaryExamples are a MS Word file and display of

information on the screenSequential access (one record after another

from the beginning to end) versus random access

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Sequential Files 1Sequential access methodEach record is accessed one after another

from the beginning to end. Master and transaction files for updateCost saving (efficiency) and data security

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Sequential Files 2

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Indexed Files 1Random access methodConsists of a data file and its indexAn index contains the key of the data file and

the address (record number) of the corresponding record

An index is sorted based on the key values (attributes) of the data file

Find the desired key and retrieve its address, and then access the record.

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Indexed Files 2

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Hashed Files 1Random access methodUse a mathematical function for mapping a

key to the addressUser gives a key the hash function maps

the key to the address then passes to the OS record is retrieved

No need to have an indexDirect, modulo division, digit extraction, and

collision hashing

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Hashed Files 2

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File SystemsControl how data are stored and readUnix/Linux: ext2, ext3, ext4, and othersMac: HFS, HFS PlusMS Windows:

• FAT (File Allocation Table)• FAT32 • NTFS (New Technology File System)

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Directories 1A special type of file containing information

about other files A directory itself is a fileAn index telling where files are located Organized as a tree (hierarchical structure)Each directory except the root directory

has a parent directory.

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Directories 2Root directory (/)Working directory (current directory)Parent directory versus child directoryAbsolute path versus relative path/home/kucc625/wwwkucc625/www (assuming /home as a

working directory)

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Binary FilesA collection of data stored in the internal

format of the computer.Use all 256 (8 bits) bit-string patterns Data can be character, integer, floating-

point numbers, and/or other type of data.Object files, images, videos, sounds, and

formatted text files (e.g., MS Word file) are binary files

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Text FilesA sequence of lines and plain textsA file of characters.Each byte is written in 128 ASCII codes

(MSB is 0 and remaining 7 bits are used)Even a text file eventually stores data in 0’s

and 1’sReadable in text editors and many

applications as well

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ASCII Files 1Text format containing ASCII charactersDepending on the delimiter (separating

date items)Free format (space delimited)Comma delimited format or comma

separated values (CSV). Text in quotesTab delimited formatFixed format

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ASCII Files 2

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Files for Specific ApplicationsFormatted for specific applicationsMS Word (.doc & .docx) and Excel (.xls

& .xlsx) have their own format.Unlikely to be shared by multiple

applications.One application (program) and its specific

data format.One program-one data file?

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ReferencesForouzan, Beherouz. 2013. Foundations of

computer science, 3nd ed. Cengage Learning EMEA.