Case and דין
Generally the גמרא presents the adjudication of a specific case. That is, it tells a story = case, and then describes how the halakhic system wishes us to relate to the events described in the story = the ruling in the case.
For example, the first משנה in the second פרק of ברכות starts:
- היה קורא בתורה, והגיע זמן המקרא: אם כיוון לבו – יצא, ואם לאו – לא יצא.
The משנה presents a specific case: Someone who is reading the תורה, specifically the פרשה of Shema, and the time of hisTorah reading happens to coincide with the time that he is required to say קריאת שמע.
It then presents the adjudiction of the case: Under certain circumstances the outcome is יצא (he has fulfilled his obligation) while under other circumstances the outcome is לא יצא (he has not fulfilled his obligation).
Note: "Different circumstances" mean different specific cases.
Note: The only reason to adjudicate or render a halakhic ruling in relation to a case, is that there is a halakhic problem which has to be solved.
This structure of a case and דין or, ruling make up the basic halachik unit that is to be analyzed.
Other terms used to describe case and ruling are: מציאות or אוקימתא (case) and דין or פסק (ruling).
The structure of the relationship between case and din is "If/When (description of case)-->Then (apply the following ruling)"