# Frontend and backends

## The frontend and backends system

The **3di** system separates recorded data from the interviewing forms and reporting tools. The **frontend** provides the interview and reporting features: it’s the bit you see when you start up the **3di**. Patient data are recorded in a **backend**. There can be any number of backends – of which just one can be loaded at a time. However, *any number of cases may be stored in a single backend*. You do not need to create a new backend for each child, and indeed most users will only ever need to create a single backend to contain all cases.

The separation of frontend and backends has three important advantages:

* you can use separate backends for disparate sets of data (for the subjects in different studies, for example)
* you can benefit from software upgrades which add or improve retrieval and recording features simply by using a new frontend with your existing backends
* backends can be stored in a designated location, perhaps on a separate drive, to comply with institutional policies regarding backup and patient data security

## Selecting and creating backends

The selection and creation of backends are launched from the [**Main Menu**](https://docs.ixdx.org/using-the-software/the-main-menu).

You will create a backend as part of your training course, and in many cases you won't need to think about backends again.

## The 3di installation folder

A complete **3di** installation has the following folder organisation:

![](https://4094242155-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FnAX879uVOFdRUslo1PlM%2Fuploads%2FRD2tt8DobI37hJx3eGGp%2Finstallation-folder-2025.png?alt=media\&token=868043ac-d43c-4d48-8406-b8e18bcf7cca)

{% hint style="warning" %}
Do not:

* delete, move or rename any provided folders immediately inside your **3di** installation folder (you *can* create others)
* make any changes inside the **Resources** folder
* create folders immediately inside the **Backends** folder
* delete, move or rename the **Cases** folder within a backend, or any of the numbered case folders within (but you *can* modify or delete generated Word reports)
  {% endhint %}

The **3di** application file (frontend) sits at the top level of the 3di installation folder. In the above screenshot, it's the file named *3di5\_uk\_251219*. This is the file you double-click to launch the program.

In the installation folder you will see several subfolders. **PreEntry** and **Reference** contain various files provided by us which may be useful for reference and other purposes as described on the training course. **Resources** is part of the 3di software and should be ignored.

The **Backends** subfolder in the installation folder is special. This is known as the **backend source** – a folder containing one or more subfolders, one per backend. Backends store all of your clinical data: interview responses plus any reports you generate. It is possible to have more than one backend source (for example, you might store backends on a removable drive) and more than one backend within the same backend source (for example, to separate cases between two different clinics). However, the overwhelming majority of users will only use the default backend source folder, and a single backend within it. Switching between backends and backend sources is described in [the main menu](https://docs.ixdx.org/the-main-menu#select-and-open-backend).

For each of your backends, there is in the **backends source** a folder bearing the backend’s name which stores:

* the **backend (data) file**, which has a systematically related name: if a backend folder is called *xyz*, then it contains a backend data file called *3di2\_xyz\_be*
* a **Cases** folder containing all the output documents generated for each patient.

Output documents are themselves organised into folders with 6-digit names based on each patient’s system-assigned Case\_ID. Thus the folder *000080* stores all output documents relating to patient 80. A patient’s Case\_ID appears at the top-right of the **3di** [Case Manager](https://docs.ixdx.org/starting-an-interview#open-the-case-manager).

There is no need to navigate your file system to find a patient’s output documents: the **Case Manager** provides a **Go to documents folder** button which opens a window displaying the relevant folder.

After installing the **3di** you might link the frontend to the **Training5** backend, or ask the system to [create](https://docs.ixdx.org/the-main-menu#create-and-open-backend) and link to a new backend.

You can create a backend in the provided **Backends** folder or elsewhere on your hard disk or removable drives (such as USB pen drives). If you choose one of these alternate locations, the **3di** will generate a **Backends** source folder to contain your new backend and any further backends you subsequently create there.

## Move or copy a backend

{% hint style="info" %}
Close the **3di** before attempting to move a backend
{% endhint %}

For simplicity, we recommend you always use the single backend that you created on your training course, which will be located in the default Backends folder within your 3di installation folder.

However, the need can arise to move or copy a backend from one Backends folder to another Backends folder, which can be accomplished by the usual means in Windows Explorer. Because all patient reports generated by the **3di** are stored in subfolders of a backend folder, moving or copying a backend subfolder moves or copies those reports also.

Other than for backup purposes, it is not a good idea to *copy* a backend. There is a risk that some new patients will be added to one backend, and other new cases to the copy – and then there will be two backends with the same name but different content. Even worse, a patient who was in the backend at the time of copying may be edited in either the original or the copy – there are then two “versions” of the same case!