In a traditional Oracle e-Business Suite environment customization logic (forms, triggers, procedures etc) are directly coded in the Oracle e-Business Suite environment. Because of this the logic is directly integrated and all objects are immediately accessible.
Conversion and integration usually takes places via open interfaces (there are more possibilities of course like API's, database links, webservices, integrated SOA Gateway, etc). But usually we use a traditional conversion file, which is first loaded in a custom staging table where we do enrichment, validation and transformation before sending the information to the open interface.
How is this changed in a cloud environment?
In a cloud environment these open interfaces are still there. They are unlocked using UCM, the Universal Content Manager. Using standard import processing, which were available in Oracle eBS as well, the data from UCM is loaded into the open interfaces and imported in the Oracle tables.
The main difference with the traditional eBS environment is that all enrichment and transformation must have taken place before loading into UCM. You deliver the enriched and validated data for example through excel spreadsheets which can be loaded using File Based Data Import.
Excel sheet templates can be loaded from Oracle Enterprise Repository.
(For example templates for ERP Cloud can be found here http://docs.oracle.com/cloud/latest/financialscs_gs/OEFBF/FBDIOverview.htm#FBDIOverview)
Next to File Based Data Import the SAAS environment also provides several webservices which can be invoked directly from the external application. Usually this occurs using a middleware environment (like SOA Suite, Mulesoft etc), where enrichment and transformation takes place (and where also error handling with an error hospital is usually taken into account).
Note that File Based Data Import can also be invoked as a webservice. Using middleware you would do your enrichment and transformation and you send the excel files to UCM, which will load the open interfaces. You could even fetch some data from SAAS first to enrich the data using a webservice that invokes a BI Report to fetch the data.
In stead of developing customizations directly into the SAAS environment, customizations can be developed in a separate environment. This can be a PAAS environment. This PAAS environment can be directly linked in the SAAS environment using Integrated Pages. If the SAAS application is based on Alta-UI the user will not notice a difference between the SAAS application and the custom application providing some additional service.
To load data from the SAAS application again you can use web services. This could be a BI Report that fetches any data from the SAAS application to expose to the PAAS environment. The BI Report can be invoked as a web service.
For example you could fetch your item information based on scanned barcodes including on hand quantities etc.
Next to this actions in the SAAS environment can be triggered by web services, like creating an inventory transaction or order through a web service invoked from the PAAS environment.
Next to these integration options, Oracle also offers the Integration Cloud Service. This is a service which allows you to easily integrate SAAS to other SAAS application or On Premise applications through web services and maintain your services in this environment.
So .. still enough options to build customizations and do custom integration in cloud.