We considered two main approaches to the deployment for improvements to the web site.
The evolutionary changeover strategy (see below) was the one we decided on.
Big Bang Changeover.
Advantages and disadvantages are listed in the table.
Big Bang Changeover
The new site is developed "in the background",
leaving the existing one as it is, until the big day.
At this point, a metaphorical switch is thrown and the new site replaces the old one.
In this scenario, there is no big day.
Instead, the changeover takes place over a much longer period.
This involves a planned series of relatively small,
incremental changes to the existing site,
which will morph into the new one.
Advantages and Disadvantages
Only one significant point at which the change takes place.
Several changes over a longer period are necessary.
A well-defined target, in terms of new features.
New features and when they'll be delivered are less well-defined.
A well-defined end point to this phase of the project.
The amount of time taken to reach a specific goal is not known until much later.
Due to the required development time for the multiple
complex feature list and their inter-dependencies;
the first (big bang) date on which the site improvements will be apparent,
are further in the future.
Improvements are prioritised and staged.
Some can be introduced much earlier.
Possibility of some "quick wins" initially.
Changes are more or less permanent and unlikely to be reversible.
Changes are more flexible and reversible.
No user feedback can be obtained prior to the changeover.
Once it's done, it's done.
More user feedback can be obtained along the way,
since changes are staged and incremental.
The big changeover may take users by surprise.
They may not like the result.
Users' expectations are better managed,
though planning and notifications in good time.
The big change may disrupt users who are used to the old site.
Smaller, incremental changes are less disruptive to users.