Stereotypes

A stereotype is an annotation that you set to communicate a major decision to the EGL compiler; in most cases, to the generator invoked by the compiler. In response to the annotation, the EGL system code creates output that acts stereotypically, that is, in accordance with a pattern. The pattern differs from one stereotype to another.

The difference in generated output is often related to the statements you code. The following example clarifies the idea and includes reference to a stereotype (CSVRecord) that is available only in a commercial product:

You might define a Record part that is the basis of a record used during sequential-file access. In this case, statements such as add and update do file I/O.
Here is the Record part, which is stereotyped by the CSVRecord stereotype:
```
Record MyCSVRecordPart type CSVRecord
                            {  fileName = "employ", delimiter = "," }
   employeeID INT;
   employeeName STRING;
   salary DECIMAL(7,2);
end
```
The fileName field refers to a value that you make available used at generation time. That value identifies the file used at run time, and the delimiter field indicates how one value in the file is separated from the next.
Alternatively, you might define a Record part that is the basis of a record used during relational-database access. In this case, statements such as add and update access a database management system.
Here is the Record part, which is stereotyped by the SQLRecord stereotype:
```
Record EmployeeType type SQLRecord 
                         { tableNames = [["employee"]], keyItems = [employeeID] }

   employeeID INT      { Column     = "empid" };
   employeeName STRING { Column     = "empname"};
   salary DECIMAL(7,2) { Column     = "salary"};
end
```
The tableNames field references a database table, and the keyItems field indicates which fields are referencing a table key.

In both the preceding examples, the word “type” is an abbreviation for “stereotype.”

To see that a stereotype is a kind of annotation, compare the earlier of MyCSVRecord with the following, equivalent one:

Record MyCSVRecordPart {@CSVRecord {fileName = "employ", delimiter = ","}}
   employeeID INT;
   employeeName STRING;
   salary DECIMAL(7,2);
end

Although the second, longer form is rarely used, the at sign (@) again declares a value used by the EGL system code. In this case, the declaration is based on the CSVRecord Record part, which includes several fields:

Record CSVRecord type Stereotype
   fileName STRING;
   delimiter CHAR(1);
   ...
end

You declare a stereotype only when you define a part. If the part can include fields, the stereotype identifies a set of member annotations, which are annotations that apply to those fields. For example, consider the EmployeeType Record part again:

Record EmployeeType type SQLRecord 
                         { TableNames = [["EMPLOYEE"]], KeyItems = [employeeID] }

   employeeID INT      { Column     = "EMPID" };
   employeeName STRING { Column     = "EMPNAME"};
   salary DECIMAL(7,2) { Column     = "SALARY"};
end

The Column annotation relates the employeeID, employeeName, and salary fields with relational-database table columns; specifically, with the EMPID, EMPNAME, and SALARY columns. The SQLRecord stereotype causes the Column annotation to be available in any Record part that is defined with the stereotype.

Each classifier such as Record or Program supports zero to many stereotypes. You select from the list when you define a custom part.