1. FILE SECTION
2. WORKING-STORAGE SECTION
3. LOCAL-STORAGE SECTION
4. SCREEN SECTION
5. REPORT SECTION
6. LINKAGE SECTION
Redefines clause is used to allow the same storage allocation to be referenced by different data names.
Subscript refers to the array of occurrence, where as Index represents an occurrence of a table element. An index can only modified using perform, search & set. Need to have an index for a table in order to use SEARCH and SEARCH All.
Structured programming is a Logical way of programming, you divide the functionalities into modules and code logically. OOP is a Natural way of programming; you identify the objects first, and then write functions, procedures around the objects. Sorry, this may not be an adequate answer, but they are two different programming paradigms, which is difficult to put in a sentence or two.
IDENTIFICATION DIVISION and PROGRAM-ID paragraph are mandatory for a compilation error free COBOL program.