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Wilmington, North Carolina once had a thriving Black middle class and an elected interracial government. In 1898 white supremacists used violence to overthrow that government, kill Black residents and drive many others from the city.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
The Z notation /ˈzɛd/ is a formal specification language used for describing and modelling computing systems.[1] It is targeted at the clear specification of computer programs and computer-based systems in general.
In 1974, Jean-Raymond Abrial[2] published "Data Semantics".[3] He used a notation that would later be taught in the University of Grenoble until the end of the 1980s.
While at EDF (Électricité de France), working with Bertrand Meyer, Abrial also worked on developing Z.[4] Z was originally proposed by Abrial in 1977 with the help of Steve Schuman and Bertrand Meyer.[5] The Z notation is used in the 1980 book Méthodes de programmation.[6]
Z was developed further at the Programming Research Group at Oxford University, where Abrial worked in the early 1980s with researchers including Bernard Sufrin and Ib Holm Sørensen (1949–2012),[7] having arrived at Oxford in September 1979.[8] Sørensen received a DPhil degree from Oxford University in 1981 on early Z-based research.[9] He taught early courses in Z notation at Oxford[10] and established the Z User Meeting series, initially in Oxford.[11]
Ib Holm Sørensen led the Transaction Processing Project at Oxford University from its inception in 1982 (later renamed the "CICS Project",[12]), in collaboration with IBM Hursley.[13] The project formally specified parts of IBM's CICS transaction processing software using Z notation. This won a Queen's Award for Technological Achievement in 1992.[14][15] As part of the CICS project, Sørensen extended Edsger Dijkstra's Guarded Command Language by allowing the use of Z-schema notation as abstract commands.[16] These ideas were later formalized by Carroll Morgan in his refinement calculus.[16]
Z schema boxes were added by Carroll Morgan for the structuring of larger specifications.[17] Ian Hayes edited the 1987 book Specification Case Study on the use of Z (2nd edition published in 1993),[18] with contributions from Morgan, Sørensen, Sufrin, and others. A de facto standard for Z was produced as a book by Mike Spivey in 1989 (2nd edition, 1992).[19]
Abrial has said that Z is so named "Because it is the ultimate language!"[20] although the name "Zermelo" is also associated with the Z notation through its use of Zermelo–Fraenkel set theory.
Z is based on the standard mathematical notation used in axiomatic set theory, lambda calculus, and first-order predicate logic.[19] All expressions in Z notation are typed, thereby avoiding some of the paradoxes of naive set theory. Z contains a standardized catalogue (called the mathematical toolkit) of commonly used mathematical functions and predicates, defined using Z itself. It is augmented with Z schema boxes, which can be combined using their own operators, based on standard logical operators, and also by including schemas within other schemas.[17] This allows Z specifications to be built up into large specifications in a convenient manner.
In 1985, a series of Z Users Meetings was instigated by Ib Sørensen, initially at Rewley House in Oxford.[11] In 1992, the Z User Group (ZUG) was established at one of these meetings to oversee activities concerning the Z notation, especially meetings and conferences.[11] ZUG continued to organize regular Z User Workshops/Meetings (ZUM). Later, when they began to be held outside the United Kingdom, these became known as the International Conference of Z Users. Later still, these conferences were combined to cover the B-Method as well, becoming known as the International Conference of B and Z Users (ZB).
ISO completed a Z standardization effort in 2002. This standard[21] and a technical corrigendum[22] are available from ISO free:
Because Z notation uses many non-ASCII symbols, the specification includes suggestions for rendering the Z notation symbols in ASCII and in LaTeX. There are also Unicode encodings for all standard Z symbols.[23]
In 1992, Oxford University Computing Laboratory and IBM were jointly awarded The Queen's Award for Technological Achievement "for the development of ... the Z notation, and its application in the IBM Customer Information Control System (CICS) product."[24]
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The Z notation is a formal specification language used for describing and modelling computing systems. It is targeted at the clear specification of computer programs and computer-based systems in general.
E–Z configuration, or the E–Z convention, is the IUPAC's preferred method of describing the absolute stereochemistry of double bonds in organic chemistry. It is an extension of cis–trans isomer notation (which only describes relative stereochemistry) that can be used to describe double bonds having two, three or four substituents. E–Z notation can only be used when neither atom of the double bond has two identical atoms or substituent groups attached to it. Following the Cahn–Ingold–Prelog priority rules (CIP rules), each substituent on a double bond is assigned a priority, then positions of the higher of the two substituents on each carbon are compared to each other. If the two groups of higher priority are on opposite sides of the double bond (trans to each other), the bond is assigned the configuration E (from entgegen, German: [ɛntˈɡeːɡən], the German word for "opposite"). If the two groups of higher priority are on the same side of the double bond (cis to each other), the bond is assigned the configuration Z (from zusammen, German: [tsuˈzamən], the German word for "together"). The letters E and Z are conventionally printed in italic type, within parentheses, and separated from the rest of the name with a hyphen. They are always printed as full capitals (not in lowercase or small capitals), but do not constitute the first letter of the name for English capitalization rules (as in the example above). Another example: The CIP rules assign a higher priority to bromine than to chlorine, and a higher priority to chlorine than to hydrogen, hence the following (possibly counterintuitive) nomenclature. For molecules with multiple double bonds, locants can be included to specify the geometry of each E and Z geometric detail. For example, the chemical name of alitretinoin is (2E,4E,6Z,8E)-3,7-dimethyl-9-(2,6,6-trimethyl-1-cyclohexenyl)nona-2,4,6,8-tetraenoic acid, indicating that the alkenes starting at positions 2, 4, and 8 are E while the one starting at position 6 is Z.
The Z User Group (ZUG) was established in 1992 to promote use and development of the Z notation, a formal specification language for the description of and reasoning about computer-based systems. It was formally constituted on 14 December 1992 during the ZUM'92 Z User Meeting in London, England.
Jonathan P. Bowen (born March 14, 1956) is a British computer scientist and an Emeritus Professor at London South Bank University. His main contribution has been in formal methods, especially the Z notation. In addition, he has worked in the area of museum informatics, including the creation of the Virtual Library museums pages, an early web directory. His contributions also include works on the history of computing, especially Alan Turing.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Shirley Chisholm, elected in 1968.
