Last month’s unveiling of the Oracle Public Cloud garnered a bit of skepticism: CEO Larry Ellison claimed full support for industry standards, but analysts questioned whether it would truly be interoperable with competing clouds as Oracle insisted.

Most of the Oracle Public Cloud’s components are still unreleased, but Ars spoke with Product Marketing Vice President Robert Shimp to address questions about application portability across clouds, why Oracle chose a multi-instance architecture instead of a multitenant one, and pricing. Here's the short version on money: Oracle says pricing will be simplified and published publicly, but hasn’t revealed numbers yet. Shimp also offered some choice words for rival Salesforce.com, saying Oracle will offer greater flexibility.

The Oracle cloud is a mix of software-as-a-service (SaaS) and platform-as-a-service (PaaS) components, with one of the keys being a Java cloud service based on WebLogic. Oracle claimed customer-built applications can be moved from internal data centers to Oracle’s cloud and back again, and from Oracle’s cloud to competing ones like Amazon’s EC2. Both the technical underpinnings and licensing models will make this possible, Shimp said.

Gartner analyst Yefim Natis told Ars last month that the cloud version of WebLogic offers a subset of the full functionality available to on-premises deployments, perhaps making it difficult to move applications from an internal data center to the cloud. Separately, Constellation Research CEO R “Ray” Wang questioned whether applications will be compatible with competing clouds, given that “there are no established open standards on public clouds that we know of.”

But Shimp says customers will be able to move any application built with Java EE 5 (the version used with the Oracle Java Cloud Service) from in-house to the cloud, despite Natis’ concern about WebLogic. “There are not going to be any issues with that,” Shimp says. “There are operational distinctions between the versions that you might run in-house vs. the cloud, but that’s because you don’t need to be able to manage all the things in the cloud that you would have to do if you were doing it on-premises.”

As for moving from Oracle’s cloud to a competitor, Shimp says “there’s no distinction there. If you have an application or workload you want to run on Amazon, or Savvis, or Softbank in Japan, it’s all the same.” While some vendors are building Oracle-based clouds using Exadata or Exalogic systems, that’s not a requirement for ensuring portability, he said.

The process for uploading the application and paying for it will differ from cloud to cloud. But, “when we talk about cloud, standards are typically around operational issues, not the runtime environment of Java,” Shimp says. “Can you write an application and run it in Oracle’s cloud or Savvis’s or anybody? With a standard Java application, the runtime is all the same, so it’s not an issue.”

Beyond Java, customers who write PHP or Ruby applications for the Oracle database cloud service won’t be locked in, either, he said. In fact, customers can already run Oracle Database on Amazon, as part of a partnership between the companies. Of course, this definition of “not being locked in” assumes you want to stick with the Oracle Database in perpetuity.

Shimp chided rival Salesforce.com, noting that it uses its own programming language (Apex) and database. “Our database applications are all Standard SQL and RESTful APIs, vs. Salesforce, [which has] a unique query language. You cannot take a Salesforce database application and move it in-house,” he said.

Oracle’s multi-instance architecture

The Oracle Public Cloud uses a multi-instance architecture, with customers each running their own instances of the application. This is in contrast to multi-tenancy, in which customers share the same code. Wang argued in his blog that “Oracle will need to deliver a multi-tenant version of Fusion Middleware to provide customers with the full range of deployment option choices from on-premise, hosted, multi-instance, and multi-tenant.”

But Shimp contends that multi-instance is the wave of the future. “Multi-tenancy was pretty much the only technology you could use 10 or 12 years ago when a lot of SaaS vendors were creating products,” he says. Nowadays, virtualization makes multi-instance viable, and gives customers more flexibility, he argues.

Oracle will let customers choose from a range of options, from managing everything in-house to letting Oracle take care of patches and backups, to anything in between, he said. Customers will be able to choose different levels of isolation as well. For example, a customer might opt for dedicated hardware, but can also choose to have an isolated database that shares the same machine as other customers (presumably in exchange for a lower price, although Shimp would not confirm that).

With multi-tenancy, everyone is on the same patch schedule, and may not even get to choose when to conduct backups, he said. The multi-instance architecture also avoids complications caused by cloud customers sharing the same database, he said. Data warehousing in a multi-tenant infrastructure is difficult because “you cannot do ad hoc joins of tables in a multi-tenant database,” Shimp says.

Shimp points to a Salesforce-published document called “Salesforce Limits Quick Reference Guide,” which contains three dozen pages of things customers can and can’t do using the Salesforce cloud. “When you have a quick reference guide on what you cant do that’s 35 pages long, you know that’s a complicated system,” he says.

Pricing—just stay tuned

Of course, one might argue that Salesforce has helped to simplify the computing world for many by moving core applications to the hosted model, whereas Oracle previously resisted making a big move to the cloud. Despite making repeated jabs at Salesforce, Oracle is finally expanding its own cloud presence with the launch of the Public Cloud and the purchase of SaaS provider RightNow, and in some ways attempting to emulate its competitor.

“You’ll see pricing from us that fully recognizes the Workday, Salesforce per-head model, and try to figure out also how to seamlessly integrate that in an on-premises model,” Oracle Senior VP in the Office of the CEO Ken Glueck told Ars.

The question of when all these Oracle cloud services will become available and exactly what they will cost is still unanswered. But Shimp pledges “our pricing will be public. When you sign up, you will know what you are paying per hour, or per database or whatever. We will provide metering, so you can go online and see how much you’re using as you’re using it,” and notifications before customers reach pre-defined limits. “That level of transparency is something you won’t see from a lot of different vendors.”