Both versions are OK grammatically, but the meanings are different. Assuming you want to express a connection between the first and last halves of the sentence:

The first version, simplified, reads "We rely and we simulate." with possibly no connection at all between the two (undesirable/awkward). In the second version, "We rely, simulating..." the simulating phrase modifies the first part of the sentence, which is a direct connection indeed, as intended. It sounds quite natural and has the intended meaning.

By the way, "data" is a strange word in English. It is plural in Latin, but it is so often used like a singular noun in AmE that most people think it is like "information tonnage". It would not make sense to use "specific tonnage" to refer to a few specific items in a load of items. Instead I have seen "data points" or even "datums" (is this a "real" word?) for this use case.

Both sentence have subtly different meanings.

In our approach, we rely mainly on the page content, simulating the way a human user scans a web page for specific data.

This sentence can be read at least two different ways:

• Our approach is to rely mainly on the page content (with everything after the comma modifying the Page Content we rely mainly on.)
• Our approach is simulating the way a human user scans a web page for specific data (thus making "we rely mainly on the page content" Parenthetic.)

The path of least resistance is to interpret this sentence to mean that your approach is simulating the way human users scan a web page for specific data (by relaying mainly on page content.)

The first (and proper) sentence is a Compound Sentence held together by a Coordinating Conjunction:

In our approach, we:

1. rely mainly on the page content and
2. simulate the way a human user scans a web page for specific data.

I affirm that both are acceptable, and I see the second as slightly more sophisticated.

"Simulating" is a gerund: a noun converted to a verb with the addition of "ing". It starts the gerund phrase "simulating the way ...".

Grammatically, gerund phrases count as nouns, so your sentence breaks down to: We rely on the page content, [large compound noun].

I.e. your gerund phrase becomes an item in the list of things on which you rely.

The first sentence is a compound sentence and 'WE' is the subject of coordinate clause beginning with "simulate the way, and, of course, there is a subordinate clause beginning with(as/by which/in the like manner)a human user... data. It means:

Our approach is to show you the page content and how to navigate it as like a human user.

Before we embark on analysing the second option, the '—+ing' form used here is a participle. Simply put "+ing" form of verb discharge four functions depending on usage.

• to make tense

• to work as noun

• to work as adjective

• to work as pure noun(the +—ing + of)

In our example it is a present participle (adjective). Such +—ing formed participles have no subject. It mostly has its subject in the preceding clause to which it refers.

•The boy(who is) standing at the gate, is my brother.

But such construction often takes us unawares. As —

•I saw a dead cow walking along the street.

We know how to rearrange the sentence meaningfully. Begin the sentence with ' walking along the stree,'.

In the second sentence simulating refers to ' page content', and, thus, drastically changing the meaning. I think we have somehow make you understand the use of participle phrase. Would It not be better to place "simulating... data" after " in our approach"? In that case both the sentences mean exactly the same.