Data Structure & File Systems Hun Myoung Park, Ph.D., Public Management and Policy Analysis Program Graduate School of International Relations International University of Japan

Outline  Data Structure  Language Translators  Software Development  Software Analysis and Design  Programming  Implementation & Maintenance  Documentation 2

Data Type  Abstract data types (ADT) include  Stack (LIFO)  Queue (FIFO)  Tree and graph  Primitive type: number, string, boolean  Composite type (bundling of elements): array and record 3

Data Structure  A 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”  Arrays, records, and linked lists.  Array (fixed-size sequence of elements) vs. list (variable size) 4

Data Structure: Array  A 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] 5

Data Structure: Record  A collection of related elements (fields or attributes) of an entity  The 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, …) 6

Data Structure: Linked List  “A collection of data in which each element contains the location of the next element.”  Consists of data and link  Data contain information to be processed  Link contains a pointer (address) that identifies the next element in the list.  The last element contains data only (null pointer) 7

File Structure  “An external collection of related data treated as a unit”  Used to store data permanently in a secondary storage device or auxiliary  Examples are a MS Word file and display of information on the screen  Sequential access (one record after another from the beginning to end) versus random access 8

Sequential Files  Sequential access method  Each record is accessed one after another from the beginning to end.  Master and transaction files for update  Cost saving (efficiency) and data security 9

Indexed Files  Random access method  Consists of a data file and its index  An 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. 10

Hashed Files  Random access method  Use a mathematical function for mapping a key to the address  User give a key  the hash function maps the key to the address  then passes to the OS  record is retrieved  No need to have an index  Direct, modulo division, digit extraction, and collision hashing 11

File Systems  Control how data are stored and read  Unix/Linux: ext2, ext3, ext4, and others  Mac: HFS, HFS Plus  MS Windows: FAT (File Allocation Table), FAT32, NTFS (New Technology File System) 12

Directories 1  A special type of file containing information about other files  A directory itself is a file  An index telling where files are located  Organized as a tree (hierarchical structure)  Each directory except the root directory has a parent directory. 13

Directories 2  Root directory (/)  Working directory (current directory)  Parent directory versus child directory  Absolute path versus relative path  /home/kucc625/www  kucc625/www (assuming /home as a working directory) 14

Binary Files  A 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 (MS Word and Excel files) are binary files 15

Text Files  A sequence of lines and plain texts  A 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’s  Readable in text editors and many applications as well 16

ASCII Files  Text format containing ASCII characters  Depending on the delimiter (separating date items)  Free format (space delimited)  Comma delimited format or comma separated values (CSV)  Fixed format 17

Files for Specific Applications  Formatted for specific applications  MS 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? 18