Cursor

Enhanced Definition

In the mainframe context, a **cursor** primarily refers to the visual position indicator on a 3270 terminal screen (or emulator) that shows where the next character will be entered. It also denotes a logical pointer used in database systems like DB2 or IMS to navigate and process rows or segments within a result set or database.

Key Characteristics

- Visual Indicator: On 3270 screens, it's typically an underscore or block that highlights the current input position, indicating where user input will appear.
- User-Controlled: Users can move the screen cursor using keyboard keys (e.g., Tab, Enter, arrow keys) to navigate between fields or lines within an application or editor.
- Programmatically Controllable: Applications (e.g., CICS programs using BMS, TSO/ISPF services) can explicitly set the cursor's position on the screen to guide user input or highlight specific data.
- Database Pointer (DB2): In DB2, a cursor is a named control structure that allows a host program (like COBOL or PL/I) to process a set of rows returned by a SELECT statement one row at a time.
- IMS Navigation: Conceptually, IMS database calls (DL/I) use a form of cursor-like positioning to navigate through segments based on established parentage and search arguments.
- Types of DB2 Cursors: DB2 supports various cursor types, including scrollable, non-scrollable, sensitive, insensitive, read-only, and updatable, each with specific behaviors regarding data changes and navigation.

Use Cases

- Interactive Data Entry: Users navigating ISPF panels or CICS transaction screens to input data, where the screen cursor indicates the active field awaiting input.
- Text Editing: Editing JCL, COBOL source code, or data files within the ISPF editor, with the cursor marking