My mistakes

Archive for October 2007

Internet bots, also known as web robots, WWW robots or simply bots, are software applications that run automated tasks over the internet. Typically, bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human editor alone. The largest use of bots is in web spidering, in which an automated script fetches, analyses and files information from web servers at many times the speed of a human. Each server can have a file called robots.txt, containing rules for the spidering of that server that the bot is supposed to obey.

In addition to their uses outlined above, bots may also be implemented where a response speed faster than that of humans is required (e.g., gaming bots and auction-site robots) or less commonly in situations where the emulation of human activity is required, for example chat bots.

Bots are also being used as organization and content access applications for media delivery. Webot.com is one recent example of utilizing bots to deliver personal media across the web from multiple sources. In this case the bots track content updates on host computers and deliver live streaming access to a browser based logged in user.

Advertisements

A web crawler (also known as a web spider or web robot) is a program or automated script which browses the World Wide Web in a methodical, automated manner. Other less frequently used names for web crawlers are ants, automatic indexers, bots, and worms (Kobayashi and Takeda, 2000).

This process is called web crawling or spidering. Many sites, in particular search engines, use spidering as a means of providing up-to-date data. Web crawlers are mainly used to create a copy of all the visited pages for later processing by a search engine that will index the downloaded pages to provide fast searches. Crawlers can also be used for automating maintenance tasks on a website, such as checking links or validating HTML code. Also, crawlers can be used to gather specific types of information from Web pages, such as harvesting e-mail addresses (usually for spam).

A web crawler is one type of bot, or software agent. In general, it starts with a list of URLs to visit, called the seeds. As the crawler visits these URLs, it identifies all the hyperlinks in the page and adds them to the list of URLs to visit, called the crawl frontier. URLs from the frontier are recursively visited according to a set of policies.

In computer science, reflection is the process by which a computer program of the appropriate type can be modified in the process of being executed, in a manner that depends on abstract features of its code and its runtime behavior. Figuratively speaking, it is then said that the program has the ability to “observe” and possibly to modify its own structure and behavior. The programming paradigm driven by reflection is called reflective programming.

Typically, reflection refers to runtime or dynamic reflection, though some programming languages support compile time or static reflection. It is most common in high-level virtual machine programming languages like Smalltalk, and less common in lower-level programming languages like C.

At the lowest level, machine code can be treated reflectively because the distinction between instruction and data becomes just a matter of how the information is treated by the computer. Normally, ‘instructions’ are ‘executed’ and ‘data’ are ‘processed’, however, the program can also treat instructions as data and therefore make reflective modifications.

With higher level languages, when program source code is compiled, information about the structure of the program is normally lost as lower level code (typically machine language code) is produced. If a system supports reflection, the structure is preserved as metadata with the emitted code.

In languages that do not make a distinction between runtime and compile-time (Lisp, Forth and MUMPS, for example), there is no difference between compilation or interpretation of code and reflection.

 more… 

In general, a namespace is an abstract container providing context for the items (names, or technical terms, or words) it holds and allows disambiguation of items having the same name (residing in different namespaces).

As a rule, names in a namespace cannot have more than one meaning, that is, two or more things cannot share the same name. A namespace is also called a context, as the valid meaning of a name can change depending on what namespace applies. Names in it can represent objects as well as concept, whether it is a natural or ethnic language, a constructed language, the technical terminology of a profession, a dialect, a sociolect, or an artificial language (e.g., a programming language)….

For many programming languages, a namespace is a context for identifiers. In an operating system, an example of namespace is a directory. It contains items which must have unique names. In the Java programming language, items that appear in namespaces have a short (local) name and unique long “qualified” names for use outside the name space. Also, some languages (such as C) combine namespace and names in a process called name mangling in order to eradicate ambiguity.

more….

Name mangling (more properly called name decoration, although this term is less commonly used) is a technique used to solve various problems caused by the need to resolve unique names for programming entities in many modern programming languages.It provides a way of encoding additional information about the name of a function, structure, class or another datatype in order to pass more semantic information from the compilers to linkers.

The need arises where the language allows different entities to be named with the same identifier as long as they occupy a different namespace (where a namespace is typically defined by a module, class, or explicit namespace directive).

Any object code produced by compilers is usually linked with other pieces of object code (produced by the same or another compiler) by a type of program called a linker. The linker needs

a great deal of information on each program entity. For example, to correctly link a function it needs its name, the number of arguments and their types, and so on.

read more…