---
url: /reference/ui/delta.md
---
# Delta Perspective

The main purpose of the **Delta** perspective is to calculate a *delta*, i. e. compare two snapshots of a system
with each other. A snapshot is defined by a point in time and a branch
for which Teamscale retrieves the corresponding commit in the version
control system as well as all related quality data. The comparison of
two snapshots reveals the differences in terms of code changes, metric
changes and findings churn as well as information on whether the
code changes have been tested.

\[\[toc]]

## Types of Delta Computations

Teamscale can compute two types of delta:

* a *commit-range* delta (i.e., *»what happened between commit1 and commit2«*), and
* *merge-request* delta (*»what would happen if I merge commit1 on top of commit2«*).

The commit-range delta requires two commits as input. These commits
should be in a linear commit history (the baseline/start commit should
be an ancestor of the end commit). The input for a commit-range delta
can be configured in the *Linear History* tab of the *Delta Parameters
Page*.

The merge-request delta also requires two commits as input. They can be
configured in the *Merge Request* tab of the *Delta Parameters Page*.
You can choose any two different commits from the project repository.
Teamscale will compute a preview of the estimated effects that accepting
the corresponding merge request would have on the repository (which
findings would be added to the target branch, which commits would be
merged, etc.).

Since the configuration options and available views for the two types of
deltas are similar, we focus on describing the commit-range delta.

## Action: Calculate Delta

To calculate a delta, you can navigate to the **Delta** perspective which will open up the
*Delta Parameters Page*.

##### Delta Parameters Page

On this page you can configure the delta you would like to calculate:

![Delta Parameters](../../../howto/performing-delta-analysis/delta-parameters.png)

The table below describes the available options. If branch support has been enabled for the underlying
project, you can also compare snapshots from two different branches with
each other. Click `Compute Delta` to start the delta analysis.

## Action: Inspect Changed Files

After calculating the delta, the sidebar of the perspective will appear:

![Delta Sidebar](./delta-sidebar.png)

It automatically
redirects you to the *Changed Files Page*. This page gives you an overview which files in the repository were
»affected« within the selected interval of the
delta:

![Delta Affected Files](./delta-affected-files-zoom.png)

The page provides you a **Code Churn Summary** indicating how many
files were added, changed, deleted or moved/copied. The latter is
identified with Teamscale's own origin analysis
[\[1\]](#paper-incremental-origin) which reveals
if a file was copied from an existing file (either identically or with
small changes) or moved between locations. Further more, the page shows
you all **Affected Paths** . If you click on
a path, it will redirect you to the [Code File View](../metrics/codefile/index.md#code-file-view).\
If a file has been changed, indicated by the **Change type**,
you can click on it to open the Code Comparison View to examine the differences.

## Action: Inspecting Repository Changes

The sidebar provides a link to the *Repository Change Page*.

This pages provides an overview of all commits which took place within
the time interval of the delta. The page contains the activity stream of
commits in the same way as the *Activity View* of the **Activity** perspective.
Browsing the stream of commits is particularly useful if you want to find the
root cause of a metric change as [described here](../../../howto/monitoring-quality-evolution/#finding-the-root-cause-for-a-trend).

##### Change Treemap Page

While the Changed Files Page shows the code changes in the delta
in a list format, the Change Treemap Page provides the same information in treemap form:

![Change Treemap for Delta](./delta-change-treemap.png)

The image shows such change treemap.
Red indicates files which were deleted during the delta, blue
indicates changed files and green indicates added files.

## Action: Viewing the Test Gap Treemap

To get an overview over which changes contained in the
delta have been tested and which might have been missed, you can use the *Test Gap
Treemap Page*.

##### Test Gap Treemap Page

![Test Gap Treemap for Delta](./delta-testgap-treemap.png)

The image shows a test gap treemap for a given delta. This treemap works just like the [Test Gap
Treemap Widget](../dashboard/widgets/#test-gap-treemap-widget) in the dashboard.
It is already configured with the start and end date provided
in the delta parameters. Every rectangle represents a method in the system. Gray indicates
methods which were not changed in the selected time frame,  green indicates added or
changed methods which have been tested (and the test coverage has been uploaded to Teamscale),
and red and orange indicate untested methods that have been added or changed
within the selected time frame, respectively. Also just like in the dashboard,
the `Execution only` toggle shows test coverage irrespective
of changes, and `Hide unchanged methods` makes small changes in
large systems easier to locate by hiding all gray areas.

## Action: Viewing Metric Changes

The **Delta** perspective does not only provide information about code churn and the corresponding commits, it also
contains the delta with respect to quality data. In
particular, it provides the **Metric
Churn** . Use the left sidebar to navigate to
the corresponding page.

##### Metric Churn Page

This page shows the delta for each metric, comparing the metric value at the end of
the selected time interval with the metric value at the selected
baseline.

![Delta Metrics](./delta-metrics-table.png)

The image shows the table indicating
the **Metric Churn** . For each metric, it
provides the name as well as the delta change.
If the checkbox at the bottom is checked it also displays the absolute metric value.

Each row can be clicked to open a dialog showing the history and treemap for the respective metric:

![Delta Metric Dialog](./delta-metrics-dialog.png)

#### Navigating the Findings Churn

In addition to code churn and metric churn, the **Delta** perspective also provides the
findings churn. Use the left sidebar to navigate to the
*Findings Churn Page*.

##### Findings Churn Page

This page gives you an overview of findings which were added ( **New
Findings** ) and which were removed ( **Removed Findings** during the selected
time interval. Additionally, it also
shows you findings in code which was changed during the time interval.
This is relevant if you selected
quality goal *improving* for your project. Under this
quality goals, findings in changed code should be removed on-the-fly.
Hence, this page shows you the opportunities you missed.

![Delta Findings Churn](./delta-findings-churn.png)

The table
provides the message, the
finding location as well as the finding group. Clicking on
the messages opens the [Findings Detail View](../findings/index.md#findings-detail-view) of the **Findings** perspective,
clicking on the location
redirects you to the [Code Detail View](../metrics/codefile/index.md#code-file-view).

Additionally, the sidebar offers the same [filter mechanisms](../findings/index.md#findings-overview-table) to navigate
the findings as the **Findings** perspective: You can filter by entering a
regular expression or by selecting specific finding categories or finding groups.

You can also select multiple findings by clicking on the checkboxes and then right-click to perform actions on all findings at once.

![Delta Findings Churn Context Menu](./delta-findings-churn-context-menu.png)

***

#### Further Reading: