Middleware is a software layer that offers sophisticated features to developers -- transactions, security, clustering, etc. -- so they can focus on building their custom applications instead of solving those hard problems repeatedly. But middleware is only "static" software in the sense that you still have to configure it, deploy it on servers, manage and monitor it, which was typically left to IT teams to do.
PaaS is a superset of middleware and offers all these good middleware services to developers, in addition to covering the operational aspects that were typically owned by IT teams.
How would you handicap the PaaS market at this point, particularly some of the bigger players?
The four big Java middleware companies are IBM, Oracle, VMware and Red Hat, and it's very interesting to watch their PaaS strategies. They understand the market is going toward cloud, but that's not where their strength is -- it's in private data centers. These large legacy vendors are conflicted on how to protect their legacy business while also embracing the cloud.
The one that has made a bold move in the cloud is VMware with Cloud Foundry. The company has a history of being proprietary and private, but when they did a PaaS, they open sourced it. Now they've rolled that into their Pivotal Initiative, along with big data research. They still have a conflict between service and software, though. Red Hat is as conflicted as VMware, deciding in November that its OpenShift would be fully private. They're clearly focusing on their strength in the data center.
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What about Salesforce.com and Microsoft? They seem like big PaaS players, too.