|
|
|
Home fly
Home fly may trams fir a disease but with that disease it may provide medicine also. The prophet Mohammed PBUH said It the home fly falls in your drink then dip the whole fly into the drink pull it out because on one of its wings there may be a...
Questions For An Alchemist
Questions for An Alchemist: By Robert Bruce Baird: INSPIRATIONAL COMMENTS: The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst...
Start here...first principles (D)
Start here…first principles (D) Terry Dashner……………Faith Fellowship Church, PO Box 1586 Broken Arrow, OK 74013 What’s the foremost law of science? Norman Geisler and Peter Bocchino raise this question in their book entitled, Unshakable Foundations...
The future of the Human Species - Part 1: Are we in danger?
The sun, that celestial body which has always fascinated the human species, which differentiates night and day, which when angry, produces the fascinating auroras, is father to us all: humans, animals and plants. The sun is the father of life on...
'They' Value the Menstruum
The Templar flag Columbus and da Gama traveled under was the dominant economic and therefore (if for no other reason) force in the three centuries before they set sail. Not just in Europe as we have shown, but in the entire world, these progeny of...
|
|
| |
|
|
|
|
|
|
Declarative Programming - Strategies for Solving Software Problems
Many software and hardware producers take pride in the
exponential pace of technology change, but for users and
consumers of their products and services the rapid technological
obsolescence often means increased costs, frustrations, and
unfulfilled promises. Corporate America expects to make capital
investments in goods and facilities that should last five, ten,
even twenty years, but only an eighteen-month lifetime for
computer software and hardware investment is not uncommon.
Lowering the costs to develop new software solutions or
extending the lifetime of software applications are two
complementary approaches to addressing technological change.
These goals can often be met by taking a declarative strategy
when designing software systems independent of the programming
methodology employed.
Issues with Imperative Programming
Most programming projects today use the imperative style of
programming. Developers write sequences of operations in a
language, such as C++, Java, Visual Basic, etc., that implement
an algorithm, or recipe, for performing tasks. The algorithm for
the task mixes logical, or relational, statements about the task
to be solved and control statements about how to calculate the
solution. The logical statements describe "what-to" calculate
while the control statements describe "how-to" calculate.
Debugging the algorithm consists of verifying the accuracy of
the logical statements and fixing the control statements, if
necessary.
There are many problems with the imperative approach. The
sequence of operations critically determines the correctness of
the algorithm. Unexpected execution sequences through an
algorithm caused by user input actions or real-time events in a
multitasking environment may result in subtle or catastrophic
algorithm failure. Writing the control logic is the programmer's
responsibility and, therefore, subject to implementation errors.
Understanding a program's algorithm is often difficult for other
developers without extensive metadata, or comments, on the code
and empirical tracing of the program's execution with sample
data. Verifying program correctness consumes a significant
portion of the development effort, but also usually fails to
discover a significant number of defects.
To address the problems associated with imperative programming,
the computer industry has developed and advocated many
approaches. Structured programming and campaigns against "go-to"
statements address some of the problems discovered with ad hoc
control structures and statements. Modularization initiatives
stress decomposition techniques on the premise that humans can
better comprehend, reason about, and maintain smaller pieces of
code. Object-oriented programming advocates program
constructions using reusable components, libraries, and
frameworks. The pattern programming school stresses analogies to
other fields, such as architecture, by constructing programs
using well-designed and crafted solutions, or patterns, that
recur in many programming contexts.
What is Declarative Programming?
Declarative programming separates the logic, or what, of an
algorithm from the control, or how, of an algorithm. The
programmer still specifies the logic or equations specifying the
problem's relations, but the programming system is responsible
for control, or how the logic is evaluated. The most familiar
examples are spreadsheets and query languages for relational
databases. The user, or programmer, specifies a mathematical
relation as a query, say in SQL, for what to retrieve, while the
database engine determines how to execute the query against the
database.
There are many advantages to declarative programming over the
imperative style. In declarative languages, programmers do not
specify sequences of operations, but only definitions or
equations specifying relations. Unlike imperative programming,
the logic relations in declarative programming are execution
order independent, free of side effects of evaluation, and
semantically clear to visual inspection.
The declarative family of programming languages has a long
history in the academic computer science community and
specialized areas of commercial application, such as compiler
construction, expert systems, and databases. Declarative
languages have two main family trees. The logic declarative
languages, such as Prolog, are based on first-order predicate
calculus, which generalizes the notions of Aristotelian true or
false values to statements, or predicates, involving relations
among any entities. The other family branch consists of
functional declarative languages, such as Miranda, Haskell, and
SML. The functional declarative languages are based on the
l-calculus developed by the mathematician, Alonzo Church in the
1930's. l-calculus formalizes the notions of recursive
application of pure functions to computable problems. Although
not widely known as such, the latest programming fashion, XSLT,
an extensible stylesheet language for transforming XML, is also
a functional declarative language.
Despite the theoretical advantages of declarative programming
languages, they do not have widespread use in commercial
programming practice despite an attempt in the 1980's by Borland
to mass-market a PC version of Prolog along with the highly
popular Turbo Pascal. There are many factors contributing to the
infrequent use of declarative languages. A large contributor is
the paucity of collegiate training in declarative languages, but
awkward syntaxes of some languages, inefficient compilers and
run-times, and restricted domains of applicability of
generalized "how-to" mechanisms are all contributors.
Using Declarative Strategies in Commercial Software
While declarative programming languages have not
received
wide-spread commercial usage, the strategy of separating logic,
or what, from control, or how, in an algorithm is a powerful,
generalized technique for increasing ease of use and extending
the longevity of software. Declarative techniques are
particularly powerful in user interfaces and application
programming interfaces (APIs) that have a rich, complex set of
inputs over a relatively small field of execution behaviors.
Two examples of commercial software that illustrate the
applicability of declarative techniques are DriverLINX and
ExceLINX in the fields of data acquisition and test instrument
control.
Using Declarations for Data Acquisition
DriverLINX is an API for controlling data-acquisition hardware
used to measure and generate analog and digital signals
interfaced to all types of external transducers.
Data-acquisition applications include laboratory research,
medical instrumentation, and industrial process control.
Traditionally, APIs for data-acquisition devices modeled the
characteristics of the hardware design and had a large number of
functions of one or more parameters to setup the hardware and
control data flow through the system. The ordering of sequences
of operations was often critical to correctly programming and
controlling the hardware. Upgrading to new data-acquisition
hardware was often costly as hardware-necessitated changes in
the order of operation sequences to program the hardware
required costly software changes.
To surmount these problems, DriverLINX takes an abstract and
declarative approach to data-acquisition programming. Instead of
modeling specific board designs, DriverLINX abstracts the
functional subsystems of data-acquisition hardware into
generalized attributes and capabilities. Programs request the
measurement task they want to perform by parameterizing a
"service request" declaration. The DriverLINX runtime determines
how to satisfy the service request using the available hardware
and returns the measurements as a packetized stream to the
program. The data-acquisition programmer is relieved of any
responsibility for data-acquisition algorithm control.
Besides relieving the programmer of control responsibility, the
DriverLINX abstract, declarative approach gives the program
syntactic and semantic interchangeability when migrating to
equivalent hardware products. The abstract, declarative approach
also helps isolate the software vendor from early technological
obsolescence of change in the computer industry by focusing on
the immutable logic of data-acquisition relations while the
control mechanisms vary with software developments. DriverLINX
has been a viable approach to data-acquisition programming for
more than 12 years despite the market evolution from 16-bit
Windows to .NET today.
Using Declarations for Test Instruments
Test instruments, such as digital voltmeters and electrometers,
have evolved from simple devices with a front panel knob and
display screen to sophisticated measurement processors
performing dozens of measurement and control functions. Like
data-acquisition devices, typically developers send a carefully
ordered sequence of commands to an instrument to setup the
measurement and then send additional command sequences to
control the data flow of measurements from the instrument. The
aforementioned problems for developers using imperative
approaches to instrument control significantly limit ease of use
and prohibit quick instrumentation solutions to short-term
measurement needs.
ExceLINX is an add-in to Microsoft Excel that allows rapid
specification of instrument test setups by using worksheet
forms. Users specify, or declare, the channels, configurations,
sampling rates, triggering, and data locations for the
measurements they wish to perform by filling out an Excel
worksheet. When the user selects the "start" button on the
toolbar, ExceLINX translates the specification into the correct
command sequence for the target instrument, initiates the
measurement, and flows the data back to the requested worksheet.
Users can setup and collect measurements by themselves in
minutes using logic specifications compared to days or weeks
using programmer's time for imperative specifications.
Internally, ExceLINX also uses a declarative approach to
handling the complex problem of field validation for the
worksheet forms. Instruments have hundreds of parameters with
complex overlaps among parameters. To validate whether the
instrument supports the parameter set the user selected,
ExceLINX maintains a dependency tree of allowed, disallowed, and
unused parameters for every input cell on the worksheet. Each
node in the tree also maintains logical relations among the
selected set of parameters that ExceLINX evaluates at runtime to
cross validate user input selections. Each supported instrument
model has different parameter semantics, but ExceLINX can easily
handle this complexity by switching model trees because the
model-specific logic in the validation tree is separate from the
shared control implementation in the ExceLINX code.
Declarative programming strategies that separate logic from
control in algorithms are powerful techniques that can be used
with today's popular imperative languages. These techniques can
make software more interchangeable, maintainable, usable, and
endurable
Copyright Roy E. Furman, M.D., Ph.D 2005
About the author:
Roy Furman, M.D., Ph.D. is Director of Research and Development
at Scientific Software Tools, Inc. He leads a team of software
developers who have produced over 70 commercial software
products for customers in the test and measurement, life science
and healthcare industries. Visit their website,
http//www.sstnet.com for articles and information on software
development.
|
|
|
|
|
| Science/AAAS | Scientific research, news and career information |
| International weekly science journal, published by the American Association for the Advancement of Science (AAAS). |
| www.sciencemag.org |
|
| Science/AAAS | Table of Contents: 1 December 2006; 314 (5804) |
| This Week in Science: Editor summaries of this week's papers. Science 1 December 2006: 1349. ... 2006 American Association for the Advancement of Science. ... |
| www.sciencemag.org |
|
| Science.gov : FirstGov for Science - Government Science Portal |
| Science.gov is a gateway to government science information provided by US Government science agencies, including research and development results. |
| www.science.gov |
|
| ScienceDaily: Your source for the latest research news and science ... |
| ScienceDaily -- the Internet's premier online science magazine and science news web site -- brings you the latest discoveries in science, health & medicine, ... |
| www.sciencedaily.com |
|
| Science News - New York Times |
| Find breaking news, science news & multimedia on biology, space, the environment, health, NASA, weather, drugs, heart disease, cancer, AIDS, mental health ... |
| www.nytimes.com |
|
| Science News Online |
| Weekly magazine offers featured articles from the current issue along with special online-only features. Includes photo collection, archives, ... |
| www.sciencenews.org |
|
| Science in the Yahoo! Directory |
| Explore the fields of astronomy, biology, geology, mathematics, and physics and all of their related disciplines with resources designed for professionals, ... |
| dir.yahoo.com |
|
| Open Directory - Science |
| Agriculture (2454); Anomalies and Alternative Science (525); Astronomy (4208); Biology (20593); Chemistry (4852); Computer Science@ (2358) ... |
| dmoz.org |
|
| BBC - Science & Nature |
| The best of BBC Science and Nature, from TV and radio, to the web and beyond. Take a tour from the smallest atoms, to the largest whales and the most ... |
| www.bbc.co.uk |
|
| Science - Wikipedia, the free encyclopedia |
| Sciences versus Science: the plural of the term is often used but is difficult to ... Science education is also a very vibrant field of study and research. ... |
| en.wikipedia.org |
|
| Popular Science |
| Monthly magazine about current science and technology. |
| www.popsci.com |
|
| Science/AAAS | ScienceNOW: The Latest News Headlines from the ... |
| AAAS web magazine. Some free sample stories, subscription required for full text. |
| sciencenow.sciencemag.org |
|
| ScienceCareers.org | Science Jobs, Funding, Meetings, and Advice ... |
| Searchable database of jobs, sorted by field specialty. Can post resume and curriculum vitae. Includes tips for improving the workplace for employers and ... |
| sciencecareers.sciencemag.org |
|
| American Association for the Advancement of Science |
| Research news, issue papers. Educational programs, science policy (US and international). |
| www.aaas.org |
|
| NASA - Science@NASA |
| News and features about NASA research, aimed at the general public. Includes sections on astronomy, space science, beyond rocketry, living in space, ... |
| science.nasa.gov |
|
| Science NetLinks: Resources for Teaching Science |
| Resources for K-12 science educators. |
| www.sciencenetlinks.com |
|
| Cool Science for Curious Kids |
| Fun and interactive site to help kids appreciate science. Why are snakes like lizards, and monkeys like moose? Find out here. |
| www.hhmi.org |
|
| Welcome to the Science Museum |
| London museum and library of science. Exhibitions cover all areas of science and technology. Includes online exhibits and a learning area. |
| www.sciencemuseum.org.uk |
|
| New Scientist - International News, Ideas, Innovation |
| Weekly science and technology news magazine, considered by some to be the world's best, with diverse subject matter. Articles from current issue and ... |
| www.newscientist.com |
|
| CNN.com - Science and Space |
| Offers news stories related environmental issues, archeology, astronomy, technology, geology and other science topics. |
| www.cnn.com |
|
|