Part 2

Strings over an alphabet set

Strings are defined over an alphabet set.  An alphabet set is simply a set of entities, and can be alphanumeric characters, special characters, or even  abstract types.

Now let’s define some notation:

If Σ (pronounced as “sigma”) is an alphabet set, then Σ*("sigma star") are all the strings over that alphabet.  Σ* is also the same as Str (Sigma) in RESOLVE notation.

Example 1:

If Σ consists of True and False, then we write:

Σ = B = {T, F} and

Σ * = {empty_string, <T>, <F>, <T, F>, <T, T, F...>, …}

 As you see all the strings over the boolean set B is a very large set.

Example 2:

If Σ consists of 0 and 1, then we write:

Σ = {0, 1} and then Σ * will be all binary strings and an empty_string

Σ * = {empty_string, <0>, <1>, <0, 0>, <0, 0, 0, 1..>, …}