By Gio Wiederhold, Updated 28 Jan 2001.
Representation
Representation Character set: Discussed earlier Numbers: unary, binary, decimal Complexity of representation for human comprehension: George Miller: The Magical Number 7 ± 2 Structure:
linear (DNA) ; Language, logical sequential reasoning parallel processing: many units doing the same thing (easy to program) SETI@home, protein folding at home , harder if partitions are diverse hierarchical - divide and conquer - from one viewpoint networks: intersecting hierarchies Example Bill-of-Materials Processing BOMP Parts per supplier, parts for assembly of space shuttle 2D: images, memory, pattern matching, 2.5D: Stereo ; multiple angles, focus, Polaroid glasses 3D: folded protein, real-world objects, engineering models, holograms for visualization
Number representation -- decimal vs, binary
Counting with only two symbols {0, 1} . (need a reference to reading?).
Why Binary numbers?
What is the benefit of Binary Number representation. reliability through simplicity.
Counting with only two symbols {0, 1} .
What about 10 {0, .. , 9}?
What about 3 {-1,0,+1}?
Other base systems: 10, 3,
...
Character sets: ASCII 7 bits = 128
characters - 33 for control. (32 + null)
Derived from teletypes. Leaves 95 printable characters
In practice 8 bits = 256 choices, ASCII plus whatever someone wants.
For more extensive languages there is Uniciode 16 bits 64K choices (1K is 1024 -- why)
Build characters to words or numbers; words or numbers to records or sentences; records or sentences to messages; messages to papers or books; papers or books to knowledge?
Many formats. Easily ambiguous. Y2K problem.
Use letters for months in international communication! Nearly the same.
Origin of names of months/
Anything on the web is international.
Bit Image: Encodings of 2D graphics as height x width pixels -- each pixel has 3 x intensity of color (RGB) or (Luminosity, .. ) A variety of standards, GIF, BMP, JPEG (why)
For viewing 3D representation has to be converted to 2D, b y software or hardware [SGI -- Jim Clark's first company] What about 3D bit images? What about movies?
For ARPAnet and continuing: Requests for comments (RFCs) to proposals, collected at SRI International. Implemented and adopted by the community, after discussion, when effective.
Example: SMTP (RFC 8xx): combined messy Telnet and FTP operations into a simple email protocol.
Alternate means of developing standards
Implement, show, convince others of usefulness and leverage if major company (now Microsoft, formerly IBM)
Committee of wise men, supported government mandates. Governments can set standards, but are rarely competent to do so. Politicians and marketers think it's simple, like electric plugs.
Commercial value of getting one's standard accepted. Standards are a major commercial competitive weapon.
Now we have a surfeit of standards (look at video storage), confusion, cost, dirty tricks.
Standards take long to develop, criticize, implement, get the bugs ou
Then they stick around for a long time, often too long.
Two-horse Roman chariot -> grooves in limestone street --> all carts --> mines --> steam-propelled mine carts -> RRs -> BART.
The various protocols communication differ in terms of
For all projects, since it is concerned with business: Give a motivation in terms of benefits—that can be money, or public good.
If it is a public good, still who would pay for it?
If advertising is a source of income, how would you collect income:
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