There are many database options available for middle-tier databases, because they essentially store temporary data. This is in contrast to EIS-tier databases that are often seen as databases of record, which are expected to last "forever." When you are considering a database product for an EIS-tier database, it is reasonable to choose a relational database product from a well-known, established company.
In contrast, middle-tier databases - because they are temporary - open up the possibilities of using technologies that might significantly improve performance and reduce development as well as maintenance costs.
Listed below are the two primary reasons to consider middle-tier persistence, along with reasons why the databases are temporary:
- Persistent cache in the middle tier. The data stored in the middle-tier only is what is needed to support the processing in the middle tier. All the data is eventually written to the EIS-tier database.
- Consolidated data in the middle tier. This data is consolidated only in the middle tier. You can think of it as "publishing" a catalog to the middle tier. Much like a catalog, the data in the middle tier may be there for weeks, months, or even a year - but it is very unlikely to be there for years or decades as in the case of a master database.
The options for middle-tier databases include:
- SQL-92 relational databases
- SQL:1999 object-relational databases
- Object-relational mapping for SQL-92 or SQL:1999 databases
- Object-oriented databases
- XML databases
- XML middleware
