Listing four elements is a means of analysing the comparison, not a rule that every sentence must contain four independent words. Speakers may omit a marker or the shared aspect for rhetorical force.
In “al-ʿilm ka-l-nūr” (“knowledge is like light”), both terms and the marker appear. The point of likeness can be understood as clarifying what was obscure or dispelling ignorance.
In “al-ʿilm nūr” (“knowledge is light”), both terms remain but the marker is absent. The force of guidance or illumination is communicated more directly.
Method: identify the intended comparison, assign the four analytical roles, then determine which are verbally expressed and which depend on implication or context.