SAP comes loaded with all the extras. Among the extras that are most helpful to IT managers are all the access routines needed to pull any business object that managers can think of out of SAP databases. However, SAP has not thought of everything where your particular applications are concerned. SAP organizes its standard database tables to service business units based on conventional business applications. It’s likely your business requires something new, perhaps even something exotic. In that case, you will need to create a new database, using information from different places. Basically, you need a logical database. You need to create a virtual business data object repository consisting of a new kind of record or table that suits your purposes. In addition, the repository should be composed of information that is actually stored in a number of different locations, none of them necessarily logically associated with one another. Let’s take a closer look at creating logical databases.

A case for a logical database
Suppose my company manufactures widgets of the most obscure variety, and they are components of other widgets. I sell my widgets as raw material for the more sophisticated widgets built by others, but in some cases I actually partner with other manufacturers in creating yet another class of widget. Now, in my world, I consequently have customers who are also partners. I sell to them and I partner with them in manufacturing and distribution. Also, I need an application that uses both of these dual-use relationships.

Essentially, I have a customer database and a partner database. Neither contains records that are structured to contain the identifying particulars of the other. Thus, I need a hybrid database that gives me tables detailing these hybrid relationships. What can I do? I can go the long way around and write a new database, pulling information from both and creating new objects with a customized program that I write by hand. However, this process is cumbersome and contains maintenance issues. On the other hand, I can use SAP’s logical database facility, create my logical database in a couple of minutes, and have no maintenance issues at all.

Logical database structures
There are three defining entities in an SAP logical database. You must be clear on all three in order to create and use one.

  • Table structure: Your logical database includes data from specified tables in SAP. There is a hierarchy among these tables defined by their foreign keys (all known to SAP), and you are going to define a customized relationship between select tables. This structure is unique and must be defined and saved.
  • Data selection: You may not want or need every item in the referenced tables that contributes to your customized database. There is a selection screen that permits you to pick and choose.
  • Database access programming: Once you’ve defined your logical database, SAP will generate the access subroutines needed to pull the data in the way you want it pulled.

Creating your own logical database
ABAP/4 (Advanced Business Application Programming language, version 4) is the language created by SAP for implementation and customization of its R/3 system. ABAP/4 comes loaded with many predefined logical databases that can construct and table just about any conventional business objects you might need in any canned SAP application. However, you can also create your own logical databases to construct any custom objects you care to define, as your application requires in ABAP/4. Here’s a step-by-step guide:

  1. Call up transaction SLDB (or transaction SE36). The path you want is Tools | ABAP Workbench | Development | Programming Environment | Logical Databases. This screen is called Logical Database Builder.
  2. Enter an appropriate name in the logical database name field. You have three options on this screen: Create, Display, and Change. Choose Create.
  3. You’ll be prompted for a short text description of your new logical database. Enter one. You’ll then be prompted to specify a development class.
  4. Now comes the fun part! You must specify a root node, or a parent table, as the basis of your logical database structure. You can now place subsequent tables under the root table as needed to assemble the data object you want. You can access this tree from this point forward, to add additional tables, by selecting that root node and following the path Edit | Node | Create. Once you’ve saved the structure you define in this step, the system will generate the programming necessary to access your logical database. The best part is you don’t have to write a single line of code.

Watch out!

The use of very large tables will degrade the performance of a logical database, so be aware of that trade-off. Remember that some tables in SAP are very complex, so they will be problematic in any user-defined logical database.

Declaring a logical database
Here’s another surprising feature of logical databases: You do not assign them in your ABAP/4 Code. Instead, the system requires that you specify logical databases as attributes. So when you are creating a report, have your logical database identifier (the name you gave it) on hand when you are defining its attributes on the Program Attributes screen. The Attributes section of the screen (the lower half) will include a Logical database field, where you can declare your logical database.

Logical databases for increasing efficiency
Why else would you want to create a logical database? Consider that the logical databases already available to you begin with a root node and proceed downward from there. If the data object you wish to construct consists of items that are all below the root node, you can use an existing logical database program to extract the data, then trim away what you don’t want using SELECT statements—or you can increase the speed of the logical database program considerably by redefining the logical database for your object and starting with a table down in the chain. Either way, you’ll eliminate a great deal of overhead.