element that is the composition of snapshots
(situations) in time. Situoid is a combination of
infinitesimal slices, where each slice is a situation
framed by its initial and final timestamps, i.e. a
situation is a projection of a situoid on time
boundaries. A Situoid is composed by situations that
satisfy the configuration of a set of rules among
events changing the contextual elements.
Definition (Contextual Element): In this work we
refer to a structural entity (an endurant) that
participates in a context as a contextual element to
avoid the overloaded use of the term entity, having
similar meaning to an infon. A contextual element
can be perceived as a complete concept even if we
were able to freeze time. A context is composed of
one or more contextual elements.
Definition (Context): Context is “what can be said
about an entity in its environment, i.e. context does
not exist by itself. The context of an entity may have
many constituents, called context conditions.
Examples of context conditions of a person are the
person’s location, mental state, and activity.
Together, these context conditions form the entity’s
context.” (Costa, 2007). Context refers to the data
elements being perceived from the observed world,
i.e. the first level of the SA theory (Wickens, 2008).
A context can be represented using a structural
modelling language, i.e. context model is a
conceptual model of context. Analogous to the
ontological categories of moment in UFO (intrinsic
and relational), we define two main categories of
context: intrinsic context and relational context. An
intrinsic context belongs to the essential nature of a
single entity, not depending on relationships with
other contextual elements, e.g. the body temperature
of a person. On the contrary, a relational context
depends on the relation between different entities.
Definition (Event): An event (or perdurant) is an
occurrence. An event can be atomic or complex. An
atomic event occurs in a moment in time, does not
last, i.e. its begin and end time points are the same.
A complex event is an individual composed of other
event instances, i.e. it accumulates temporal parts,
extending in time (Guizzardi et al., 2013). An event
is responsible for the transition between states of a
contextual element. Examples of events are: an
increase of a patient’s body temperature, the arrival
of an ambulance, a recommendation of
hospitalization and a bite of a mosquito. Events are
responsible for the lifecycle of a relationship (or
relator in OntoUML), i.e. a relationship exists
according to the occurrence of events. For example,
the event of a health professional giving first aid to a
patient can initialize an instance of a treatment
relationship between the patient and a health unit.
This instance depends on other events to keep their
existence, such as the patient taking medicine.
Definition (Situation): “A situation is a special
configuration which can be comprehended as a
whole and satisfies certain conditions of unity
imposed by certain universals, relations and
categories associated with the situation” (Herre and
Heller, 2005). Comprehension refers to the second
level of the SA theory, i.e. the understanding on how
the data elements perceived (contextual elements)
relate to each other in a way that it can be
recognized as a whole. Therefore, comprehension is
the reasoning capability of the phenomena observer
– in SML context the software designer and domain
experts. Universals refer to the homonymous
category in UFO. A situation is a part of the reality
that can be comprehended as a whole, has duration
and can be past (we use the term deactivated) or
current (actived). Therefore, a situation is an
individual that is composed by other individuals,
including the states of contextual elements and other
situations, constrained by formal and temporal rules.
For example, in the situation of “John being infected
with Zika”, the contextual elements are John, Zika
and (possibly) an Aedes mosquito. The event that
triggers this situation is the bite of the mosquito on
John skin, followed by the event of the virus
entering in John’s blood flow.
We classify simple and complex situation as
fundamental categories, avoiding the use of the term
type to reflect the abstraction of a domain-related
situation, the initial idea of ST. In order to address
this abstraction of types of events, types of situations
and their causal relations, we employed the multi-
level theory embedded in UFO-MLT (Carvalho et
al., 2015). We say that situation and event are
individuals, while situation type and event type are
first-order types. Thus, an event is instance of (iof)
an event type, while a situation iof a situation type.
“A mosquito biting a person” is an instance of an
event type. “A mosquito biting John’s skin in a
specific moment” is an instance of an event and, by
transitivity, is iof that event type. Similarly, the
situation type of “possible contagion of Zika within
a geographical area” is a powertype of the situation
of “a contagion of Zika in Brazil in 2016”. With this
distinction, we can abstract causal relationships
among types of event and situation, e.g. the event
type of “a mosquito biting a person” can cause the
situation type of “possible contagion of Zika”.