Edit intro based on reviews

[loayshaqir1]

We edited the introduction.ipynb file based on the feedback we received from new people combined with Ahmad & Mahmoud's feedback.
Here are the list of questions/ things to clarify that we received:

• Why when registering ie functions there is a yield statement instead of a simple return?
• Did not understand how py_rgx_string outputs X,Y (where does it get them from?)
• Missing example that shows the difference between py_rgx_string and py_rgx_span.
• Explain how data is stored and when it gets computed, explain the lazy evaluation of rules.
• Add more explanation to why we get an empty tuple when we query a relation that has no free variables (all constant) when the statement is true vs why we get nothing when its false.

So we edited the introduction file and added explanations to answer all of the above questions

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[DeanLight]

In theory, we usually say that a datalog/rgxlog query is trying to find all instantiations of the free variables that satisfy the query.

And this is why if we have a query with no free variables, we get an empty set of instantiations if its true and no such set if its false.

Perhaps you can present queries using the instantiation notation and then the explanation here will be easier to understand.

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[DeanLight]

I dont think this "empty table" will persist in later versions, and are queries even saved in the DB?

What the users should know here is that we save the facts in the database, the rules' logic is saved seperately and only evaluated lazily (on demand).

One a query is issued, the engines uses the rules to derive all possible solutions from the existing facts that would satisfy the query.

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[DeanLight]

why is this error message here?

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[DeanLight]

added some comments

[DeanLight]

Why is this here? should we not install NLP in this case?

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[DeanLight]

I would rewrite the second sentense "A query is essentially a way to retrieve specific information from a dataset, i.e it finds all instantiations of the free variables that satisfy the query. " the second part of the sentence is not an example of the first part, so the use of "ie" is incorrect.

Maybe just say that querying in rgxlog uses the same synatx and semantics as DataLog. Under said semantics, we try to find all instantiations of free variables that satisfy the queried relation.

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[DeanLight]

address my 2 small comments and then you can merge,