The fundamental characteristic that distinguishes a strong entity from a weak entity is its ability to be uniquely identified. A strong entity possesses its own primary key, which is an attribute or set of attributes that uniquely identifies each instance of the entity. Conversely, a weak entity does not have a sufficient set of attributes to form a primary key on its own. Its existence is dependent on a strong entity, and its unique identification is achieved by combining its own partial key (discriminator) with the primary key of the owner (strong) entity. Therefore, the structure and self-sufficiency of the primary key is the core differentiator.

A. Association: Both strong and weak entities participate in associations (relationships) with other entities; this is not a distinguishing feature.

C. Foreign key: While a weak entity's primary key incorporates a foreign key from its owner, strong entities also use foreign keys to establish relationships.

D. Cardinality: This describes the numerical aspect of a relationship (e.g., one-to-many) between entities, not the intrinsic nature of the entity itself.

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1. Elmasri, R., & Navathe, S. B. (2017). Fundamentals of Database Systems (7th ed.). Pearson. In Chapter 7, Section 7.3, "Weak Entity Types," it states: "Entity types that do not have key attributes of their own are called weak entity types... The primary key of a weak entity type is formed by the primary key of the owner entity type, plus the weak entity type’s partial key." (pp. 223-224).

2. Silberschatz, A., Korth, H. F., & Sudarshan, S. (2020). Database System Concepts (7th ed.). McGraw-Hill. In Chapter 7, Section 7.5, "Weak Entity Sets," the text explains: "An entity set that does not have a primary key is referred to as a weak entity set... The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent, plus the weak entity set’s discriminator." (p. 285).

3. Stanford University. (n.d.). CS145 Introduction to Databases, Notes: The Entity-Relationship Model. Stanford Online. Retrieved from the course materials which state: "A weak entity can be identified uniquely only by considering the primary key of another (owner) entity... The primary key of the weak entity set is the combination of the primary key of the owner entity set and the discriminator of the weak entity set."