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Integration

Introduction

What

Can explain integration

Combining parts of a software product to form a whole is called integration. It is also one of the most troublesome tasks and it rarely goes smoothly.

Approaches

Late-and-One-Time vs Early-and-Frequent

Can explain how integration approaches vary based on timing and frequency

In terms of timing and frequency, there are two general approaches to integration: late and one-time, early and frequent.

Late and one-time: wait till all components are completed and integrate all finished components near the end of the project.

This approach is not recommended because integration often causes many component incompatibilities (due to previous miscommunications and misunderstandings) to surface which can lead to delivery delays i.e. Late integration → incompatibilities found → major rework required → cannot meet the delivery date.

Early and frequent: integrate early and evolve each part in parallel, in small steps, re-integrating frequently.

A can be written first. This can be done by one developer, possibly the one in charge of integration. After that, all developers can flesh out the skeleton in parallel, adding one feature at a time. After each feature is done, simply integrate the new code into the main system.

Here is an animation that compares the two approaches:

Big-Bang vs Incremental Integration

Can explain how integration approaches vary based on amount merged at a time

Big-bang integration: integrate all components at the same time.

Big-bang is not recommended because it will uncover too many problems at the same time which could make debugging and bug-fixing more complex than when problems are uncovered incrementally.

Incremental integration: integrate a few components at a time. This approach is better than big-bang integration because it surfaces integration problems in a more manageable way.

Here is an animation that compares the two approaches:

Exercises

Top-Down vs Bottom-Up Integration

Can explain how integration approaches vary based on the order of integration

Based on the order in which components are integrated, incremental integration can be done in three ways.

Top-down integration: higher-level components are integrated before bringing in the lower-level components. One advantage of this approach is that higher-level problems can be discovered early. One disadvantage is that this requires the use of stubs in place of lower level components until the real lower-level components are integrated into the system. Otherwise, higher-level components cannot function as they depend on lower level ones.

Bottom-up integration: the reverse of top-down integration. Note that when integrating lower level components, may be needed to test the integrated components because the UI may not be integrated yet, just like how top-down integration needs stubs.

Sandwich integration: a mix of the top-down and bottom-up approaches. The idea is to do both top-down and bottom-up so as to 'meet' in the middle.

Here is an animation that compares the three approaches:

Exercises