Automated HTML Scaper - in Julia

I wanted a really lightweight way to generate a set of rules to find a specific HTML node without having to either code the rule for it or parse HTML laboriously to find it.

The idea is that, for a specific HTML document (say a web page), using a web UI, I can "tag" the piece of text I'm looking to extract and then auto-generate a set of rules to find the immediate parent node of that tagged text. That means every new instance of this HTML document, I can simply execute the rule set to find the node I'm looking for, regardless of the new content.

Illustration

As always, this is probably explained using an example.

Let's say we have the following HTML document containing stock price data that we're looking to extract

<div>
    <section>
        <h6>Stocks</h6>
        <ul class="Stocks">
            <li>GOOG</li>
        <ul>
        <h6>Prices</h6>
        <ul class="prices">
            <li>254.34</li>
        </ul>
    </section>
</div>

Let's say we are looking to scrape two data elements from this document: Stock Name and Stock Price. For our auto-rule generator to work, using an (as yet undeveloped) UI to highlight the relevant data on our HTML document by wrapping the relevant info in an HTML tag.

...
<li><bx-tag name="Stock Name">GOOG</bx-tag></li>
...
<li><bx-tag name="Stock Price">254.34</bx-tag></li>

The rule generator will look specifically for bx-tag html tags and work up the HTML tree to generate a rule to find it. For example, for Stock Price, a psuedocode version of the rule set could look something like:

stock_names = String[]
from root:
    find `section` tag
    find `ul` tag at index 0
    foreach child `li` tag:
        append inner text to stock_names

We could generate a rule also for prices, the only difference being the index at which to find the ul tag.

bx.jl will be smarter than this however, and the rule generator will search for the first uniquely identifiable tag as it climbs up the HTML tree using a combination of indexes and HTML element attributes.

So for our Stock Name rule, we could actually be left with something far simpler:

from root:
    dfs for `ul` tag with class="stocks"
    foreach child `li` tag:
        append inner text to stock_names

This is far more useful for webscraping as page updates are very likely to chop and change HTML element indexes, so finding elements by attribute is far more effective.

Bx.jl objects