Group:
sequences
Topic:
access by current position
Topic:
disk allocation
Topic:
encryption
Topic:
file directory
Topic:
file input/output
Topic:
global declarations and variables
Topic:
immutable files and data
Topic:
loosely structured data
Topic:
read-only and write-once file systems
Topic:
temporary data objects
Topic:
translation of data
Topic:
uniform representation of files and sequences
Topic:
unique numeric names as surrogates
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Summary
Files are a sequence of data records on an external medium. The model for files is magnetic tape but most are now located on disk. Operating systems keep files device independent and include keyboard input files and printer output files. Files often have internal structures despite their one dimensional representation. The internal structure is usually hierarchical since pointer structures require explicit indices. Components may be fixed length or delimitated by record headers. In Cobol, the program's data division describes each file in detail. Files are accessed by current position; with a reset function for "rewinding" the file, and an end-of-file predicate. Many files may be randomly accessed, or randomly positioned followed by sequential access. (cbb 5/80)
Subtopic: file as byte sequence 
| Quote: a UNIX file is a string of characters; the user controls its format and interpretation
| | Quote: a file is a sequence of bytes; not a sequence of records [»ritcDM7_1978b]
| | QuoteRef: wirtN1_1971 ;;58 procedures put, get reset for I/O functions odd (x), eof (file) and int (character) and chr (integer), succ and pres of scalar list
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Subtopic: file as sequence
| Quote: a file is an ordered sequence of elements without format; all formatting by higher-level modules or programs [»daleRC_1965]
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Subtopic: first-class values
| Quote: files in OS6 are first-class values; access heading and body by file handle; heading contains information about file [»stoyJE3_1972]
| | Quote: OS 6 streams are first class objects; assign to variables, use as parameters, returned by stream functions; e.g., RemoveLayoutChs to remove layout from a stream [»stoyJE3_1972]
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Subtopic: file names
| Quote: a file has one, symbolic name that is arbitrarily long and descriptive [»daleRC_1965]
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Subtopic: files as interface between programs
| Quote: in most operating systems, the interface between programs is disk files or pipes
| | Quote: most operating systems run sequence(s) of program activations; free resources and store data in disk files between activations [»wirtN9_1989]
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Subtopic: avoid files
| Quote: the information world should be without files; i.e., interconnections, multiple versions, and multiple views are easily visible [»nelsTH12_1986]
| | Quote: users of file systems must keep track of files and the cluttered relationships between them [»nelsTH1_1988]
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Subtopic: files as database of records
| Quote: a database does not see files as character arrays; perhaps database functions should be the low level facility [»stonM7_1981]
| | Quote: Cobol's data division provides physical and logical descriptions of files [»sammJE_1969, OK]
| | QuoteRef: vanwA_1969 ;;183 files consists of books, maxpage, maxline, and maxchar
| | Quote: Jackson bases program structure on the data structures of serial files [»jackMA_1975]
| | Quote: the serial file is the fundamental data structure; explored sequentially
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Subtopic: chronological files
| Quote: instead of using end-of-file, introduce end-of-day markers to initiate once a day processing [»jackMA5_1976]
| | Quote: many files are serial because they are chronologically ordered [»jackMA_1975]
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Subtopic: immutable files
| Quote: with immutable files, the file is not a container of variable information [»giffDK3_1988]
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Subtopic: encrypted files
| Quote: gives a secure user encryption scheme for files; notes difficult problems with human engineering and protecting keys [»gudeE9_1980, OK]
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Subtopic: avoid pointers in files
| Quote: by requiring strong assignment (var<-val) for files, files can not use reference values [»demeA3_1979]
| Quote: as persistent storage, files cannot contain pointers nor carry their own types
[»buneP5_1986]
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Related Topics
Group: sequences (7 topics, 97 quotes)
Topic: access by current position (7 items)
Topic: disk allocation (32 items)
Topic: encryption (45 items)
Topic: file directory (55 items)
Topic: file input/output (21 items)
Topic: global declarations and variables (33 items)
Topic: immutable files and data (59 items)
Topic: loosely structured data (20 items)
Topic: read-only and write-once file systems (8 items)
Topic: temporary data objects (6 items)
Topic: translation of data (26 items)
Topic: uniform representation of files and sequences (14 items)
Topic: unique numeric names as surrogates
(67 items)
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