Specification of Reactive Hardware/Software Systems - Electronic ...

2.3 Specifications, Models and Views 17
The duration of communications, the duration between communications and the
duration of data transformations are captured in timing views. Current methods
that offer timing views, be it in a very restricted way, are HOOD [Rob92], HRT-
HOOD [BW95], OOSE [J
92], OOD [Boo91] and the method of Hatley and Pirbhai
[HP88]. The Statemate method does not support timing views directly. However,
time is expressible in an adequate way within the state-transition view of Statemate.
The same holds for the SDL-based methods [Tur93, BH93] and for ROOM [SGW94].
A conceptual view focuses on classes of system components (called objects) together
with the conceptual relations that exist between those classes. These static views
are typically supported by most object-oriented methods nowadays [R 91, C 94,
CY91a, CY91b, J 92, Boo91, Mor94, SM88].
In architectural views the physical system structure is described. Examples of physical
structures are software layering, physical topologies, distributed architectures
and hardware/software partitionings. Most current specification methods aim
at the development of software and do not offer architectural views that are adequate
for hardware too. Methods that do offer architectural views are the Statemate
method [H 90] and the method of Hatley and Pirbhai [HP88]. The formal descrip-
tion techniques based on LOTOS, SDL and Estelle [Tur93, BH93, Pir92, D
89] as
well as the ROOM method [SGW94] do not offer separate architectural views,
but can adequately describe architecture within their unified model. Architecture
plays a crucial role within reactive hardware/software systems and requires
adequate modelling concepts. These are studied in Section 2.5 and in Chapter 5.
The unified model combines the five views, by describing as many system aspects as
possible simultaneously in an integrated way. Only few specification methods aim at
the development of such an explicit unified model. These are the formal description
techniques based on LOTOS, SDL and Estelle [Tur93, BH93, Pir92, D
89], the ROOM
method [SGW94] and the ROOA method [Mor94]. The formal description techniques
and ROOM, however, do not create separate views. The ROOA method, on the other
hand, produces a unified model as well as separate views.
This thesis focuses on the higher levels of specification and design (see Section 2.6).
Although each of the elements shown in Figure 2.1 are addressed in this thesis, the focus
will be on those elements that we consider most important and difficult for these higher
levels of specification and design. These elements are behavioural views, architectural
views and the unified system model. The modelling concepts that are required to support
these views are described in more detail in Section 2.5.
Behavioural views and architectural views are indispensable for
reactive hardware/software systems. Other important views are
timing views, requirements views and conceptual views.