Thursday, July 30, 2009

Grady Booch: about Linux, and TTY interfaces

Reading through Grady Booch's latest blog post, I found that Grady has shared interesting information about TTY interfaces in Linux, and of UNIX based systems.

I read the article, which Grady pointed, almost completely and found it a great read.

Something interesting to share, I thought!

Saturday, July 18, 2009

Niklaus Wirth: On current state of software development, and future

Navigating from Dr. Niklaus Wirth's wikipedia web page, I could find a very interesting interview conversation, Dr. Wirth had, on the following web site (ref,

This interview is dated, in 1997. I found Dr. Wirth's views in this interview, quite good to read.

Something interesting to share, I thought!

Sunday, July 12, 2009

Niklaus Wirth: On recursive algorithms

I have started reading the computer science, classic collection "ALGORITHMS + DATA STRUCTURES = PROGRAMS" by Niklaus Wirth. Dr. Wirth wrote this text in 1975. It's a great book.

Though "recursive algorithms" are widely known to computer science community since long time, I still could find some good advice in Dr. Wirth's book on usage of recursive algorithms.

Dr. Wirth mentions:
"An object is said to be recursive if it partially consists or is defined in terms of itself. Recursion is a particularly powerful means in mathematical definitions. The power of recursion evidently lies in the possibility of defining an infinite set of objects by a finite statement. In the same manner, an infinite number of computations can be described by a finite recursive program, even if this program contains no explicit repetitions."

We all know, what recursive algorithms are. It's a widely known programming technique. But I found particularly the advice, "When not to use recursion" in Dr. Wirth's book very worth while to apply.

Dr. Wirth further mentions:
"Recursive algorithms are particularly appropriate when the underlying problem or the data to be treated are defined in recursive terms. This does not mean, however, that such recursive definitions guarantee that a recursive algorithm is the best way to solve the problem.

Programs in which the use of algorithmic recursion is to be avoided can be characterized by a schema which exhibits the pattern of their composition. Such schema's can described as following:

P => if B then (S; P)

or, equivalently

P => (S; if B then P)

Dr. Wirth illustrates this principle with a well known, recursive definition of the factorial computation (mentioned below):

F0 = 1
F(i+1) = (i + 1) * f(i)

Dr. Wirth maps the factorial problem with the recursive anti-pattern he defines ([1] above):

P => if I < n then (I := I + 1; F := I * F; P)
I := 0; F := 1; P

In the above definition [2], S (ref, [1]) refers to,
I := I + 1; F := I * F

Dr. Wirth in the book, illustrates a following, iterative definition of factorial computation:

I := 0;
F := 1;
while I < n do
begin I := I + 1; F := I * F

Dr. Wirth says, "The lesson to draw is to avoid the use of recursion when there is an obvious solution by iteration.
This, however, should not lead to shying away from recursion at any price. The fact that implementations of recursive procedures on essentially non-recursive machines exists proves that for practical purposes every recursive program can be transformed into a purely iterative one. This, however, involves the explicit handling of a recursion stack, and these operations will often obscure the essence of a program to such an extent that it becomes most difficult to comprehend. The lesson is that algorithms which by their nature are recursive rather than iterative should be formulated as recursive procedures."

Just thought of sharing a bit of text, from this nice book and encouraging readers to read the book!

Saturday, July 4, 2009

PsychoPath XPath 2.0 processor update

Dave Carver and I have been trying to improve the Eclipse XPath 2.0 processor (a.k.a PsychoPath) during last couple of weeks. My motivation to keep working on PsychoPath engine has been a desire, to help Eclipse and Apache (Apache Xerces-J uses PsychoPath engine for XML Schema 1.1 processing) communities to be able to have a highly compliant XPath 2.0 engine.

Dave has written today, a progress update of PsychoPath development on this blog. I feel, we now have a pretty good XPath 2.0 implementation with PsychoPath. We are continuing to work on remaining non-compliant items, with PsychoPath. The remaining non compliance cases, to my opinion are near edge cases which users don't use too often. But we'll continue to solve them, with each future day and weeks.

Update on 2009-07-11: During last couple of days, Dave Carver has made quite a few useful improvements to PsychoPath, and the W3C XPath 2.0 test suite within Eclipse. I took an update today of the latest PsychoPath sources, and the XPath 2.0 test suite, and following are the latest test results:

Total tests: 8137
Failures: 811
Errors: 48

This reflects, the test pass success rate of about 89.5%. I think, this is quite good. Lot of credit of these improvements should go to Dave Carver. Dave has single handedly, created a JUnit version of the full W3C XPath 2.0 test suite, which is in itself a great feat! Having JUnit tests, helps us tremendously to run the XPath 2.0 tests, from within Eclipse.

Update on 2009-08-09: Following are the current PsychoPath test data:
Total tests: 8137
Failures: 386
Errors: 24
This reflects a test suite pass percentage of about, 95% which looks very impressive. The test suite code coverage, is about 75-80%.
Lot of credit for the latest PsychoPath improvements should go to, "Jesper S Møller" who has recently volunteered to help improve PsychoPath with the XPath 2.0 test suite. Dave Carver is also putting in his time, on PsychoPath improvements.