Prerequisites for App Development

There are no set prerequisites for users of CHT apps, yet the following are helpful for developing CHT applications.

Test Instance

To build your own application using the Core Framework you will need an instance set up for testing. You can set up a local instance by following these instructions.

Build tool

The build tool for applications using the Core Framework is cht-conf. To set it up, follow the installation instructions. To properly use the tool you will need your application files in set locations within a folder. Once you are set up with the basic file structure you can edit the files, and rebuild the application by compiling or converting components as needed, and uploading them to your test instance.

Required skills

Building a CHT Application or altering an existing app is a technical undertaking requiring a technical skillset.

To Build an App

• Use of command line tools to compile and deploy configuration code
• XLSForms for building forms (to create contacts, add contact actions, complete tasks)
• JSON for modifying settings
• JavaScript for modifying tasks and targets

To Deploy an App

• System administration
• Database administration for CouchDB and PostgreSQL
• Familiarity with AWS including EC2 and CloudWatch
• Familiarity with Docker
• Service monitoring
• Use of command line tools

Configuration skills

Technically speaking, CHT Applications consist of JSON files, XLSForms, JavaScript code, media (images/videos), and translations. Collectively, this is referred to as “configuration code”. The following technical skills are necessary to work with all the aspects of configuration code, ordered by importance:

XLSForms and XForms

Many workflows in your application, including completing tasks and creating contacts, will be generated using ODK XForms. Many app developers use XLSForms as an easier way to generate XForms. A strong knowledge of XLSForm standard is very useful in building your own application.

JSON

JSON (JavaScript Object Notation) is a format for storing structured text. Understanding JSON will help with minor modification of existing applications.

Javascript

Many key aspects are defined with JavaScript code and expressions. This includes managing profile pages, creating tasks and targets, and setting the condition for when to show forms. Unless you are only doing minor modification to an existing application, a good understanding of JavaScript is required.

CouchDB

A free and open source NoSQL database we use to store all our data, configuration, and even the application code. CouchDB is really good at replication which is the process of sending the data to another database, such as PouchDB in the client application, and back again. Although building your own app using the Core Framework does not require knowledge or experience with CouchDB it can be useful to be familiar with general concepts as a document store.

SQL

Although the application you build uses a NoSQL database, a parallel PostgreSQL database is available in the Core Framework to make querying data easier. Familiarity with SQL is needed to set up and query the database.