I need something on the relationships of alphabet, languages and regular expressions. I know what they are and also know the relationships but can’t find some solid thingy on it. Help needed.

Never having studied Automata or Compiler, I have no idea what you’re talking about.

I got it from sorting it out in my mind over and over again.

Alphabet = finite set of symbols (a-z, 0-9. ASCII etc)

string = a finite sequence of symbols drawn from the alphabet (“a”, “aaa”, “abc”, “cbaabac” over an alphabet = {a,b,c})

Language (only lexically) = any set of strings over some fixed alphabet.

Thats pretty neat. If the students can’t get this then they need to flunk!

I forgot to add that Regular expressions is a notation to easily and compactly define a pattern by which valid strings of a language are detected.

I’ve worked with regular expressions in detail. They’re extremely useful in pattern matching and input validation. I used them in my Innova MIS. Save lots of of time.

If someone wishes to learn regular expressions, there are lots of good tutorials on the net. A simple search query returns the best ones. I personally like the treatment of REs in “Professional PHP” by Wrox Press. It’s a very compact chapter and extremely informative.

Regular expressions in PHP are good for the application side… while the regular expressions in Automata side are in a raw form i mean u define words, sentences and at the end full language…

For Shaz: Shouldnt we say that Regular Expression is representation of a language OR we define a language through Regular Expressions??

as it can be deterministic or otherwise…

I think we can ultimately design a regular expresion for FULL language…

by the way i came here to comment that we can’t access the videos on the given link :-/… As m also interested in Compiler Course…

What I meant was that if you want to learn regular expressions, the PHP professional book has a very good introduction.

I’m sure regular expressions can be used for defining whole languages but I think that would be too convoluted. Anyway, not having studied compiler OR automata, I’m in no position to say much about it.

What videos? The guy only has notes and stuff.

the following page has link for videos but thats password protected…

http://www.cs.cmu.edu/%7Efp/courses/15411-f07/lectures/01-overview.html

I’ve mailed the course assistant and asked for a link or something where we can download these videos. Hopefully, I’ll get a positive response.

We define patterns of a language through regular expressions. And patterns of a language are the valid strings.