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As indicated on the Project Background Knowledge page, the main purpose of providing visual support is twofold: to provide (1) support to a user to reduce their cognitive load (the amount of information working memory needs to process at any given time) and (2) an indication of the progress on the task that has been made thus far. Visual support will be provided by means of a webpage. This page aims at explaining how you can develop code for your MARBEL agent to create such a webpage.

Although visual support is key because of the reasons listed above, it is also only meant to be just that: support that facilitates conducting a conversation with your conversational agent. In this project, you should design conversational interaction to be the primary modality of interaction!

Requirement: You should develop a webpage which facilitates conversational interaction; in other words, your webpage design should recognize that speech-based interaction is the primary modality of interaction. As such, you should avoid using input-based interactive webpage elements such as forms, dropdown menus, or other elements focused very much on user input via a webpage.

Using Prolog to build HTML in our agent

It is important to be able to synchronize the conversational interaction and the visuals displayed on the webpage shown while talking. The MARBEL agent manages the dialog, and for that reason also is the logical place to locate the control over the visual elements. This agent uses a renderPage(Html) action in the dialog_generation.mod2g module to render a webpage; when performing this action, the Prolog variable Html therefore should be instantiated with HTML webpage code. All we need to know before we can use this action, is how to create this HTML page in Prolog.

The basic idea is that we will create essentially a single string that consists of the HTML webpage code. We will utilize a combination of Prolog, HTML and Bootstrap to generate the code for dynamic webpages. Prolog rules are used to generate our HTML code. In other words, the HTML code represented as a Prolog atom, essentially a string, is manipulated with Prolog. So what does that look like? We will first take a look at how to construct some very basic HTML code, then explain how we can add more complicated HTML code that is also using Bootstrap components, and, finally, how we can piece together these components into a complete webpage.

Generating basic HTML elements with short tags

An HTML page consists of HTML elements. HTML elements consists of HTML tags that are used to organize content on that page. Tags often come in pairs of a start and end tag. Basic HTML tags, for example, are the tags <p>YOUR PARAGRAPH TEXT HERE</p> that defines an HTML paragraph, the <h1>...</h1> defining a large heading, <b>...</b> defining bold text, etc. There are many of these basic tags which, moreover, are also short which facilitates their frequent and easy use. The idea to generate basic HTML code for these elements in Prolog is very simple: Simply use single quotes '...' to generate such an element. The table next lists a few examples:

HTML Element

HTML code

Prolog code (single quoted atom)

Large heading

<h1>This is a heading</h1>

'<h1>This is a heading</h1>'

Paragraph

<p>Some text here.</p>

'<p>Some text here.</p>'

Bold text

<b>text that is bold here</b>

'<b>text that is bold here</b>'

It is very important to use the right quote symbol in your code. For example, ‘quote’ is not the same as the 'code' quote. You need to make sure you use the straight apostrophe quote ' in code.

There are many simple, short tags where it is easiest to simply put them between single quotes to create a Prolog atom for generating the corresponding HTML code. Another class of short tags are the single tags such as '<br>' for breaking a line and '<hr>' for adding a horizontal line. These are also most easily generated by simply quoting them.

Generating more complex HTML elements with attributes

Most HTML tag pairs can be simply generated by using a start and end tag and by adding some text to create the corresponding HTML. For example, <button>Start</Button> can be used to generate a simple button saying Start. However, to unleash the full power of the HTML language, it is often useful to modify the type or style of an HTML element by adding additional attributes in the form of name="value" to the start tag. For example, the following HTML code creates a large, colored button using the class attribute and several button classes made available by Bootstrap:

<button class="btn btn-secondary btn-lg">Start</button>

By means of these and generate with the rule. The HTML code is represented in Bootstrap format, which is also clearly illustrated by examples below or on Bootstrap's documentation website (Bootstrap Documentation).

Prolog Advice: To manipulate strings and atoms in Prolog it is useful to look at documentation of the following built-in functions: atomic_list_concat, atom_concat, string_concat, append, and maplist here: https://www.swi-prolog.org/. The predicate applyTemplate is a defined predicate that will be explained below.

Prolog rules are used to add a condition to a webpage (i.e. webpage X is shown when Clause Y is true).

A Quick Prolog Walkthrough

Using Prolog rules in the html.pl file

You add a condition that checks for a particular pattern ID to a Prolog rule in the html.pl file. Other simple conditions that you can add involve counting the number of recipes that are still available while in the recipe selection phase, etc. The general form of the page lay-out rules would be something like:

myPage(Txt, Button, Html) :-
  <HERE YOUR CONDITION FOR SHOWING THIS PAGE>, 
  % e.g. while recipe is being selected (check for e.g. currently active top level pattern id), we'll display recipe features
  % below code that specifies the page layout for this context
  applyTemplate('<div class="card mx-auto" style="width:67vw">~a</div>, Text, Html),
  …
  .

There are still many options to vary. For example, you can choose the parameters for the myPage predicate that fit your approach best.

applyTemplate('Template String with ~a where you want to insert atom', Atom to Insert, Return Variable).

Example Prolog Rule for a Page

page(c10, _, Html) :-
	% Condition for when to show this page
	CONDITION X,
	% Constructing HTML page
	atomic_list_concat(['<div class="alert alert-light"><center></br><h1>Hello!</br></br>','I am ~a</h1></br></br></center></div>'], Template),
	% Get the bot's name if it has one; other call it 'your assistant'
	(agentName(Name) -> N = Name ; N = 'your recipe selection assistant'), applyTemplate(Template, N, Body),
	% Create the HTML page
	html(Body, Html).

A Quick Bootstrap Conceptual Walkthrough

Bootstrap is a useful framework for working out a display, but may not be so intuitive in combination with Prolog. We provide a short walkthrough here to explain things for you.

Let’s consider you would like to display a certain lay-out with three images side-by-side. The first step you would take is to check whether such a lay-out is specified in Bootstrap. ‘Card decks’ might be a nice option, so we first look into the code that is involved:

<div class="card-deck">
  <div class="card">
    <img class="card-img-top" src=".../100px200/" alt="Card image cap">
    <div class="card-body">
      <h5 class="card-title">Card title</h5>
      <p class="card-text">This is a longer card with supporting text below as a natural lead-in to additional content. This content is a little bit longer.</p>
      <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
    </div>
  </div>
  <div class="card">
    <img class="card-img-top" src=".../100px200/" alt="Card image cap">
    <div class="card-body">
      <h5 class="card-title">Card title</h5>
      <p class="card-text">This card has supporting text below as a natural lead-in to additional content.</p>
      <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
    </div>
  </div>
  <div class="card">
    <img class="card-img-top" src=".../100px200/" alt="Card image cap">
    <div class="card-body">
      <h5 class="card-title">Card title</h5>
      <p class="card-text">This is a wider card with supporting text below as a natural lead-in to additional content. This card has even longer content than the first to show that equal height action.</p>
      <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
    </div>
  </div>
</div>

What we want to achieve, is to render a page with the HTML code, but with a dynamic input of images. The trick is to break this down into fragments. First, we want to render a given image. In the HTML, we see that each of the three images are defined as separate cards. We will now use Prolog to generate the HTML for such a card, using a given picture URL. The aim is to connect in a single string the static HTML code and the image URL (which differs according to the context of the conversation). Let’s work with the good old Pasta Aglio URL for this example. We will define a predicate ‘imgCard’, with an arity of 1 and an arity of 2. We will give it once as a fact, specifying the HTML code:

imgCard('<div class="card"><img class="card-img-top" src="~a" alt="Card image cap"></div>').

Note that the HTML is copied, with a replacement of the contents of ‘src’, in the form of ‘~a’ which is a placeholder for the image URL. This is needed in order to dynamically add this information. We will do this with the following rule:

imgCard(Image, Html) :- imgCard(I), format(atom(Html), I, [Image]).

In this rule, the Image variable is the input and holds the URL of the image, whereas the Html variable is the output HTML code for this card. In the body of the rule, the imgCard/1 is queried to retrieve the HTML code that we already specified. Then, the URL is placed at the location with `~a' in this HTML code (in the Image variable), using the format/3 predicate.

We can now use the imgCard term to render each of the three images. For the complete display, we will combine them in the broader ‘card-deck’ option, like in the example HTML we got from bootstrap. We will do this using a self-defined Prolog term, with as input the text, button text and the three images, and as output the HTML code to render. Within this term, we will start specifying the main template, and then collect the images:

myThreeImagesPage(Txt, Button, Image1, Image2, Image3, Html) :-
  Template='<div class="card-deck">~a</div>',
  imgCard(Image1,I), imgCard(Image2,I2), imgCard(Image1,I3), 
  atom_concat(I,I2,II), atom_concat(II,I3,III), 
  format(atom(Card), Template, [III]), html(Card, Html).

Note that atom_concat is used to append the different HTML snippets for each of the images. Format is then used to plug in the HTML code where the `~a' has been specified in the Template variable (as was done for the imgCard).

The current term will display three given images on the screen. Of course, you need to make sure that the right image URLs can be displayed during the conversation, which you can do using Prolog facts in recipes.pl.

Other Add-ons You Can Try

Note that these add-ons use variable names, and functions from our version of the code, and may not align with the names you use. Make sure everything matches up properly! These are just examples, you can add anything your heart desires.

Displaying Lists

Displaying lists on a screen is a practical feature when dealing with recipe selection and ingredients / utensils per recipe. Hereby some pointers on how to make this possible.

The first step is again to look for the proper template. The bootstrap list-groups template would make a good candidate here:

<div class="card" style="width: 18rem;">
  <ul class="list-group list-group-flush">
    <li class="list-group-item">Cras justo odio</li>
    <li class="list-group-item">Dapibus ac facilisis in</li>
    <li class="list-group-item">Vestibulum at eros</li>
  </ul>
</div>

The goal here is to render the HTML code with a list of ingredients / recipes / … as input. We will again break it down, starting with specifying the list items:

myListItem('<li class="list-group-item">~a</li>').
myListItem(Txt, Html) :- myListItem(T), format(atom(Html), T, [Txt]).

The way this is defined will look familiar to you, but how are these list items combined based in a Prolog list? We will add another term for this, ‘myList/2', with as first variable the list of terms, and as second variable the HTML output:

myList('<ul class="list-group list-group-flush">~a</ul>').
myList(List, Html) :- maplist(myListItem, List, Output), atomic_list_concat(Output, String),
                          myList(T), format(atom(Html), T, [String]).
myMaplist(_,[],[]).
myMaplist(P,[A|As],[B|Bs]) :- call(P,A,B),maplist(P,As,Bs).

An alternative method is to use the built-in list group item in bootstrap, define each item then add them to a list. 

itemsList('<ul class="list-group">~a</ul>').

itemsList(List, Html) :-
maplist(listItem, List, Output), atomic_list_concat(Output, String),
itemsList(Template), applyTemplate(Template, String, Html).

listItem(Txt, Html) :- applyTemplate('<li class="list-group-item">~a</li>', Txt, Html).

Making a Bullet Point List

bulletItem(Item, Html) :- applyTemplate('<li>~a</li>', Item, Html).

bulletList(Items, Html) :-
maplist(bulletItem, Items, ItemsHtml),
atomic_list_concat(ItemsHtml, Bullets),
applyTemplate('<ul>~a</ul>', Bullets, Html).

Making Buttons

button('<button class="btn btn-light btn-lg m-3" style="font-size:1.5rem">~a</button>').

button(Content, Html) :- button(B), format(atom(Html), B, [Content]).

Adding a textbox to your page layout for testing purposes

The speech interface is fitting to the context of a user in a kitchen, but not always feasible for testing. It may take additional time for the system to process speech input, you may be in a noisy environment, and there may be speech recognition failures. Hereby a pointer to easily enable a textbox to be rendered for input.

In the ‘html.pl’ file, where you format the pages to render during the conversation, for each of the pages that you may display at any point in the conversation add the following code:

A chatbox can be added for using text instead of speech for input by adding
<div class="text-center"><p class="chatbox mx-auto"></p></div>, for example,
to the footer.

 

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