The biggest challenges facing the integrator will be transaction issues. First, transaction volume may be substantially higher, not least because a single transaction on the Web site could result in anything up to a dozen or more on back-end systems.
Scalability is therefore essential.
The Web is neither session based nor process sequential. Recovering transactions that are spread across multiple systems and resources when they fail is one area that requires particular attention. And when one Web transaction leads to multiple transactions on different back-office systems, failure of any one of those systems will also need to be handled carefully. Availability round the clock is a key requirement, but legacy systems are often operated on a batch basis, with periodic downtime for reasons such as backup and maintenance. Making these systems available 24 hours a day, seven days a week will need changes to systems and procedures, and almost certainly some sort of upgrade.