Calcul des prédicats Un article de Wikipédia, l'encyclopédie libre. Le calcul des prédicats du premier ordre, ou calcul des relations, ou logique du premier ordre, ou tout simplement calcul des prédicats est une formalisation du langage des mathématiques proposée par les logiciens de la fin du XIXe siècle et du début du XXe siècle. Le trait caractéristique de la logique du premier ordre est l'introduction : Ceci permet de formuler des énoncés tels que « Tout x est P » et « Il existe un x tel que pour tout y, x entretient la relation R avec y » en symboles : et Le calcul des prédicats du premier ordre égalitaire adjoint au calcul des prédicats un symbole de relation, l'égalité, dont l'interprétation est obligée : c'est l'identité des éléments du modèle, et qui est axiomatisée en conséquence. Le calcul des propositions est la partie du calcul des prédicats qui concerne ce qui ne contient pas les notions de variables, de fonctions et de prédicats et donc pas les quantificateurs . On se donne pour alphabet : ou . ?
The Web Origin Concept Abstract This document defines the concept of an "origin", which represents a web principal. Typically, user agents isolate content retrieved from different origins to prevent a malicious web site operator from interfering with the operation of benign web sites. In particular, this document defines how to compute an origin from a URI, how to serialize an origin to a string, and an HTTP header, named "Origin", for indicating which origin caused the user agent to issue a particular HTTP request. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. This Internet-Draft will expire on May 31, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. 1. 1. 2. 2.1.
Introduction to REST You may or may not be aware that there is debate going on about the “right” way to implement heterogeneous application-to-application communication: While the current mainstream clearly focuses on web services based on SOAP, WSDL and the WS-* specification universe, a small, but very vocal minority claims there’s a better way: REST, short for REpresentational State Transfer. In this article, I will try to provide a pragmatic introduction to REST and RESTful HTTP application integration without digressing into this debate. I will go into more detail while explaining those aspects that, in my experience, cause the most discussion when someone is exposed to this approach for the first time. Key REST principles Most introductions to REST start with the formal definition and background. Give every “thing” an ID I’m using the term “thing” here instead of the formally correct “resource” because this is such a simple principle that it shouldn’t be hidden behind terminology. Link things together
Uniform access principle Explanation The problem being addressed by Meyer involves the maintenance of large software projects or software libraries. Sometimes when developing or maintaining software it is necessary, after much code is in place, to change a class or object in a way that transforms what was simply an attribute access into a method call. Programming languages often use different syntax for attribute access and invoking a method, (e.g. obj.something versus obj.something()). The syntax change would require, in popular programming languages of the day, changing the source code in all the places where the attribute was used. This might require changing source code in many different locations throughout a very large volume of source code. Going the reverse way (from method to simple attribute) really wasn't a problem, as one can always just keep the function and have it simply return the attribute value. Many programming languages do not strictly support the UAP but do support forms of it.
hCard 1.0 Tantek Çelik (Editor, Author), Brian Suda (Author) hCard is a simple, open format for publishing people, companies, organizations on the web, using a 1:1 representation of vCard (RFC2426) properties and values in HTML. hCard is one of several open microformat standards suitable for embedding data in HTML/HTML5, and Atom/RSS/XHTML or other XML. Translations: Français • 日本語 • Русский • ภาษาไทย • 漢語 • (Add your language)Copyright and patents statements apply. See acknowledgments. Example hCards are most often used to represent people: <div class="vcard"><a class="url fn" href=" Çelik</a></div> and organizations: <div class="vcard"><a class="url fn org" href=" The class vcard is a root class name that indicates the presence of an hCard. The classes url, fn, and org define properties of the hCard. Properties Status hCard 1.0 is a microformats.org specification. Errata and Updates Background Conformance Format In General Required:
Introduction to non-blocking I/O Programs that use non-blocking I/O tend to follow the rule that every function has to return immediately, i.e. all the functions in such programs are nonblocking. Thus control passes very quickly from one routine to the next. You have to understand the overall picture to some extent before any one piece makes sense. Many objects need to wait for time to pass or for an external event to occur, but because their methods must return immediately, they can't do the obvious or natural thing. To illustrate this, let's consider a simple networking class that lets you send a file to a remote machine, assuming the connection is all set up. But in the world of nonblocking programming, you can't do this, because it loops until some external event happens (i.e. the socket accepts the whole file), which is a major no-no. You can imagine the user code calling this in a simple loop, as in the following example, which prints the file to stdout as if it were a network connection: See also:
Bottom type In type theory, a theory within mathematical logic, the bottom type is the type that has no values. It is also called the zero or empty type, and is sometimes denoted with falsum (⊥). A function whose return type is bottom cannot return any value. In the Curry–Howard correspondence, the bottom type corresponds to falsity. Computer science applications The bottom type is a subtype of all types. (However, the converse is not true -- a subtype of all types is not necessarily the bottom type.) Because the bottom type is used to indicate the lack of a normal return, it typically has no values. The bottom type is frequently used for the following purposes: To signal that a function or computation diverges; in other words, does not return a result to the caller. In Bounded Quantification with Bottom, Pierce says that "Bot" has many uses: In programming languages Most commonly used languages don't have a way to explicitly denote the empty type. See also References
RDFa RDFa (or Resource Description Framework in Attributes) is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within Web documents. The RDF data-model mapping enables its use for embedding RDF subject-predicate-object expressions within XHTML documents. It also enables the extraction of RDF model triples by compliant user agents. The RDFa community runs a wiki website to host tools, examples, and tutorials. History RDFa was first proposed by Mark Birbeck in the form of a W3C note entitled XHTML and RDF, which was then presented to the Semantic Web Interest Group at the W3C's 2004 Technical Plenary. Later that year the work became part of the sixth public Working Draft of XHTML 2.0. Although it is generally assumed that RDFa was originally intended only for XHTML 2, in fact the purpose of RDFa was always to provide a way to add a metadata to any XML-based language. <? <?
High-Performance Server Architecture The purpose of this document is to share some ideas that I've developed over the years about how to develop a certain kind of application for which the term "server" is only a weak approximation. More accurately, I'll be writing about a broad class of programs that are designed to handle very large numbers of discrete messages or requests per second. Network servers most commonly fit this definition, but not all programs that do are really servers in any sense of the word. For the sake of simplicity, though, and because "High-Performance Request-Handling Programs" is a really lousy title, we'll just say "server" and be done with it. I will not be writing about "mildly parallel" applications, even though multitasking within a single program is now commonplace. Some people will inevitably take issue with some of my comments and suggestions, or think they have an even better way. The rest of this article is going to be centered around what I'll call the Four Horsemen of Poor Performance:
Fieldings' dissertation online by vikasjee Apr 26