Requirement - Usecase - Read data from an external sub-system and present it within the application. The data would also be updated in the sub-system through other use-cases from within the application.
Is it fine using SLSB-DAO pattern ? Am trying to avoid Entity beans due to reasons such as scalability as the load increases.
I see here a depedency. How about crawling the data and creating a human readable teaser string. You can also create a schema in solr to do store information in fields. As you are not the owner of data and no need of 2 ways sync, I believe it is more to do the reading. So if say 98% you are going to read the data- then optimize it for reading. In my opinion a Solr search engine and a nightly data sync is good to go solution.
Do you really need EJB? Tell me one reason why you need the EJB and can't just do it in the servlet engine?