Social networks are built on various types of connections, known as ties or edges, that link individuals, or “nodes,” within the network. These ties are the fundamental units of social networks and can be classified sociologically and through graph theory, each revealing different properties and implications.
Graph-Theoretic Classification of Ties
In graph theory, ties (links or edges) in graphs are classified by their inherent directionality:
Symmetric Tie
A tie is symmetric if the existence of a tie between A and B logically and necessarily implies that B is tied to A. Examples include being siblings, members of the same club, or spending time together. Symmetric ties thus lack meaningful directionality. These are represented by undirected graphs.
Asymmetric Tie
A tie is asymmetric if, when we know that a tie exists from A to B, it is not a necessity for a tie to exist from B to A, though it can happen. Thus, asymmetric ties are inherently directional. They come in two flavors:
- Reciprocal: A tie is reciprocal when edges exist in both directions, indicating mutual interaction (e.g., “You like me and I like you,” or both parties regularly email each other).
- Non-Reciprocal: A tie is non-reciprocal when an edge only goes in one direction (e.g., “You don’t like me, but I like you,” or “Said ignores Tom’s Facebook friend request”).
Asymmetric ties are represented by directed graphs.
Antisymmetric Tie
A tie is anti-symmetric if, when we know that a tie exists from A to B, it means B cannot by necessity be linked back to A in the same way. This often signifies a hierarchical or authority relationship. Examples include “Omar is Isaac’s boss” or a parent-child relationship, in which if you are someone’s parent, you cannot also be their parent (you are something else to them, like a son or daughter).
Sociological Classification of Social Ties
In social network analysis, there are different ways to classify these ties, including sociological and graph-theoretic criteria. The sociological classification of social ties categorizes them into four main types: Similarities, Social Relations, Interactions, and Flows. These four types can be further grouped into states, or static situations that persist over time (similarities and social relations), and events, representing repeated processes that unfold over time (interactions and flows).
Similarities
Similarities are connections between people who have something in common. These are considered “states” because they represent static situations. Ties based on similarities are typically, and often necessarily, symmetric, meaning if person A is similar to person B, then person B is also similar to person A. There are many examples of similarities as a basis of social ties. These include propinquities like being in the same place at the same time (e.g., people who go to the same school or are in the same neighborhood), memberships like belonging to the same group or club (e.g., co-membership in clubs or being part of the same events), attribute similarities, like sharing a socio-demographic attribute (e.g., being the same gender, nationality, or ethnicity).
Social Relations
Social relations describe connections where individuals acknowledge one another via a culturally recognized “role” label or have some feeling (positive or negative) toward one another. Like similarities, these are also categorized as “states”. These ties can be symmetric, asymmetric, or antisymmetric depending on the specific type of social relation. Types of social relations based on culturally recognized roles include, most notably, kinship ties like relationships such as mother, father, sibling, cousin, or uncle. Sibling and cousin ties are often symmetric ties (if A is a sibling of B, B is a sibling of A), while parent/child or uncle/nephew ties are antisymmetric (if A is a parent of B, B cannot be a parent of A). There are also other non-kin role relations. These include relationships like friends, business partners, co-workers, or even a boss or supervisor. A boss-subordinate relationship is typically asymmetric, as authority flows in one direction and is not necessarily reciprocated. Friendships, however, can be symmetric.
Social relations can also be based on having an affective attitude toward another (either positive or negative), these include such ties based on liking, trusting, disliking, or hating someone. These are usually asymmetric; for example, you can like someone without them liking you back, but they can be reciprocal. The same goes for social relations based on a cognitive attitude toward someone, such as knowing someone or being someone’s acquaintance. These are also typically asymmetric, as you can know about someone, but that does not necessarily mean that they know about you.
Interactions
Interactions are instances in which people regularly communicate or engage in behavior directed at another person, which can be positive or negative. These are dynamic “events” that occur over time. Interactions are usually asymmetric, meaning you can send a text to someone, but they don’t have to respond; they can be reciprocal if the interaction goes in both directions. Examples of interactions include communications such as calling, texting, zooming, or exchanging messages with others. They also include helping or social support ties, such as providing advice, help, or other forms of support. Support can also be emotional, or consist of providing minor (helping someone with their groceries), or major services (lending someone a thousand dollars). Interactions can also be negative or imply dominance over others, like fighting, bullying, or engaging in other violent interactions (most extremely, killing).
Flows
Flows represent ties in which something is transmitted or passed along from one person to another. Like interactions, these are “events” that unfold over time. Flows involve directed movement, with an initiator (sender/giver) and a receiver. Social ties based on flow can be categorized by the type of thing that flows through them; these include ties based on information flows, such as communication, influence, or gossip. Information flow is a key aspect of social networks, particularly in diffusion processes. However, other ties are based on the transmission of beliefsor resources in networks, such as economic transactions.
5.3 Social Relations
Social relations describe connections where individuals acknowledge one another via a culturally recognized “role” label or have some feeling (positive or negative) toward one another. Like similarities, these are also categorized as “states”. These ties can be symmetric, asymmetric, or antisymmetric depending on the specific type of social relation. Types of social relations based on culturally recognized roles include, most notably, kinship ties like relationships such as mother, father, sibling, cousin, or uncle. Sibling and cousin ties are often symmetric ties (if A is a sibling of B, B is a sibling of A), while parent/child or uncle/nephew ties are antisymmetric (if A is a parent of B, B cannot be a parent of A). There are also other non-kin role relations. These include relationships like friends, business partners, co-workers, or even a boss or supervisor. A boss-subordinate relationship is typically asymmetric, as authority flows in one direction and is not necessarily reciprocated. Friendships, however, can be symmetric.
Social relations can also be based on having an affective attitude toward another (either positive or negative), these include such ties based on liking, trusting, disliking, or hating someone. These are usually asymmetric; for example, you can like someone without them liking you back, but they can be reciprocal. The same goes for social relations based on a cognitive attitude toward someone, such as knowing someone or being someone’s acquaintance. These are also typically asymmetric, as you can know about someone, but that does not necessarily mean that they know about you.
5.3.1 Interactions
Interactions are instances in which people regularly communicate or engage in behavior directed at another person, which can be positive or negative. These are dynamic “events” that occur over time. Interactions are usually asymmetric, meaning you can send a text to someone, but they don’t have to respond; they can be reciprocal if the interaction goes in both directions. Examples of interactions include communications such as calling, texting, zooming, or exchanging messages with others. They also include helping or social support ties, such as providing advice, help, or other forms of support. Support can also be emotional, or consist of providing minor (helping someone with their groceries), or major services (lending someone a thousand dollars). Interactions can also be negative or imply dominance over others, like fighting, bullying, or engaging in other violent interactions (most extremely, killing).
5.3.2 Flows
Flows represent ties in which something is transmitted or passed along from one person to another. Like interactions, these are “events” that unfold over time. Flows involve directed movement, with an initiator (sender/giver) and a receiver. Social ties based on flow can be categorized by the type of thing that flows through them; these include ties based on information flows, such as communication, influence, or gossip. Information flow is a key aspect of social networks, particularly in diffusion processes. However, other ties are based on the transmission of beliefsor resources in networks, such as economic transactions.