By Andrea Volpini 5 years ago

In this article, we explore how to evaluate the correspondence between title tags and the keywords that people use on Google to reach the content they need. We will share the results of the analysis (and the code behind) using a TensorFlow model for encoding sentences into embedding vectors. The result is a list of […]

In this article, we explore how to evaluate the correspondence between title tags and the keywords that people use on Google to reach the content they need. We will share the results of the analysis (and the code behind) using a TensorFlow model for encoding sentences into embedding vectors. The result is a list of titles that can be improved on your website.

Jump directly to the code: Semantic Similarity of Keywords and Titles – a SEO task using TF-Hub Universal Encoder

Let’s start with the basics. What is the title tag?

We read on Woorank a simple and clear definition.

“A title tag is an HTML element that defines the title of the page. Titles are one of the most important on-page factors for SEO. […]

They are used, combined with meta descriptions, by search engines to create the search snippet displayed in search results.”

Every search engine’s most fundamental goal is to match the intent of the searcher by analyzing the query to find the best content on the web on that specific topic. In the quest for relevancy a good title influence search engines only partially (it takes a lot more than just matching the title with the keyword to rank on Google) but it does have an impact especially on top ranking positions (1st and 2nd according to a study conducted a few years ago by Cognitive SEO). This is also due to the fact that a searcher is likely inclined to click when they find good semantic correspondence between the keyword used on Google and the title (along with the meta description) displayed in the search snippet of the SERP.

What is semantic similarity in text mining?

Semantic similarity defines the distance between terms (or documents) by analyzing their semantic meanings as opposed to looking at their syntactic form.

“Apple” and “apple” are the same word and if I compute the difference syntactically using an algorithm like Levenshtein they will look identical, on the other hand, by analyzing the context of the phrase where the word apple is used I can “read” the true semantic meaning and find out if the word is referencing the world-famous tech company headquartered in Cupertino or the sweet forbidden fruit of Adam and Eve.

A search engine like Google uses NLP and machine learning to find the right semantic match between the intent and the content. This means the search engines are no longer looking at keywords as strings of text but they are reading the true meaning that each keyword has for the searcher. As SEO and marketers, we can also now use AI-powered tools to create the most authoritative content for a given query.

There are two main ways to compute the semantic similarity using NLP:

  1. we can compute the distance of two terms using semantic graphs and ontologies by looking at the distance between the nodes (this is how our tool WordLift is capable of discerning if apple – in a given sentence – is the company founded by Steve Jobs or the sweet fruit). A very trivial, but interesting example is to, build a “semantic tree” (or better we should say a directed graph) by using the Wikidata P279-property (subclass of).

    semantic tree for Apple by Wikidata

    You can run the query on Wikidata and generate a P279 graph for “apple” (the fruit)

  2. we can alternatively use a statistical approach and train a deep neural network to build – from a text corpus (a collection of documents), a vector space model that will help us transform the terms in numbers to analyze their semantic similarity and run other NLP tasks (i.e. classification).

There is a crucial and essential debate behind these two approaches. The essential question being: is there a path by which our machines can possess any true understanding? Our best AI efforts after all only create an illusion of an understanding. Both rule-based ontologies and statistical models are far from producing a real thought as it is known in cognitive studies of the human brain. I am not going to expand here but, if you are in the mood, read this blog post on the Noam Chomsky / Peter Norvig debate.   

Text embeddings in SEO

Word embeddings (or text embeddings) are a type of algebraic representation of words that allows words with similar meaning to have similar mathematical representation. A vector is an array of numbers of a particular dimension. We calculate how close or distant two words are by measuring the distance between these vectors.

In this article, we’re going to extract embedding using the tf.Hub Universal Sentence Encoder, a pre-trained deep neural network designed to convert text into high dimensional vectors for natural language tasks. We want to analyze the semantic similarity between hundreds of combinations of Titles and Keywords from one of the clients of our SEO management services. We are going to focus our attention on only one keyword per URL, the keyword with the highest ranking (of course we can also analyze multiple combinations). While a page might attract traffic on hundreds of keywords we typically expect to see most of the traffic coming from the keyword with the highest position on Google.

We are going to start from the original code developed by the TensorFlow Hub team and we are going to use Google Colab (a free cloud service with GPU supports to work with machine learning). You can copy the code I worked on and run it on your own instance.

Our starting point is a CSV file containing Keyword, Position (the actual ranking on Google) and Title. You can generate this CSV from the GSC or use any keyword tracking tool like Woorank, MOZ or Semrush. You will need to upload the file to the session storage of Colab (there is an option you can click in the left tray) and you will need to update the file name on the line that starts with:

df = pd.read_csv( … )

Here is the output.

Let’s get into action. The pre-trained model comes with two flavors: one trained with a Transformer encoder and another trained with a Deep Averaging Network (DAN). The first one is more accurate but has higher computational resource requirements. I used the transformer considering the fact that I only worked with a few hundreds of combinations.

In the code below we initiate the module, open the session (it takes some time so the same session will be used for all the extractions), get the embeddings, compute the semantic distance and store the results. I did some tests in which I removed the site name, this helped me see things differently but in the end, I preferred to keep whatever a search engine would see.

The semantic similarity –  the degree to which the title and the keyword carry the same meaning – is calculated, as the inner products of the two vectors.

An interesting aspect of using word embeddings from this model is that – for English content – I can easily calculate the semantic similarity of both short and long text. This is particularly helpful when looking at a dataset that might contain very short keywords and very long titles.

The result is a table of combinations from rankings between 1 and 5 that have the least semantic similarity (Corr).  

It is interesting to see that it can help, for this specific website, to add to the title the location (i.e. Costa Rica, Anguilla, Barbados, …).

With a well-structured data markup we are already helping the search engine disambiguate these terms by specifying the geographical location, but for the user making the search, it might be beneficial to see at a glance the name of the location he/she is searching for in the search snippet. We can achieve this by revising the title or by bringing more structure in the search snippets using schema:breadcrumbs to present the hierarchy of the places (i.e. Italy > Lake Como > …).

In this scatter plot we can also see that the highest semantic similarity between titles and keywords has an impact on high rankings for this specific website.

Semantic Similarity between keywords and titles visualized

Semantic Similarity between keywords and titles visualized

Start running your semantic content audit

Crawling your website using natural language processing and machine learning to extract and analyze the main entities, greatly helps you improve the findability of your content. Adding semantic rich structured data in your web pages helps search engines match your content with the right audience. Thanks to NLP and deep learning I could see that to reduce the gap – between what people search and the existing titles – it was important – for this website – to add the Breadcrumbs markup with the geographical location of the villas. Once again AI, while still incapable of true understanding, helps us become more relevant for our audience (and it does it at web scele on hundreds of web pages).

Solutions like the TF-Hub Universal Encoder bring, in the hands of SEO professionals and marketers, the same AI-machinery that modern search engines like Google use to compute the relevancy of content. Unfortunately, this specific model is limited to English only.

Are you ready to run your first semantic content audit?

Get in contact with our SEO management service team now!

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