|
The ascidian (subphylum Tunicata: class Ascidiacea) fauna along the southern African
coast constitutes an important component of the sessile benthic reef fauna. Little
is known of the species composition, biodiversity and distribution of ascidians
on southern African intertidal and subtidal reefs. Past research on the ascidian
fauna of South Africa was sporadic and limited, with only about one hundred and
seventy species recorded during the last one hundred and twenty years. This is the
first taxonomic study undertaken by a South African resident scientist. The study
focused on six genera in four families (Euherdmaniidae, Polyclinidae, Pseudodistomidae
and Didemnidae) belonging to the class Ascidiacea and suborder Aplousobranchia.
Five species new to science, two Polyclinum, two Pseudodistoma and
one Polysyncraton species are described. New additional information on the
distribution of five species previously known to science, including one recorded
for the first time along the South African coast, is presented. A literature review
and comparison of the taxonomic important characteristics is made of all species
known globally for the six genera. These six genera comprise twelve Euherdmania,
fifteen Aplidiopsis, forty Polyclinum thirty-one Pseudodistoma,
six Atriolum and sixty-eight Polysyncraton species.
Keywords: Euherdmania, Aplidiopsis, Polyclinum, Pseudodistoma, Atriolum,
Polysyncraton, southern Africa, distribution, ascidian, taxonomy
This research is concerned with the assessment of the usability of computer systems.
The aim of this research is to be able to take a system and assess it’s usability.
Furthermore, the methods used should provide a broad overview of the usability without
getting involved in excessive detail. Lastly, the techniques should be useful in
design rather than after implementation. In order to do this a categorisation of
usability problems was first obtained.ty of a computer system is based on this categorisation.
The assessment is divided into the following four analyses: 1) Socio/Political Analysis,
2) Learning Analysis, 3) Usefulness Analysis, and 4) Accessibility Analysis. The
main thrust of this research is providing tools for Accessibility Analysis. The
analysis is divided into the following areas, namely, a) Integration Analysis, b)
Goal Analysis, and c) Interaction Analysis. New tools to highlight usability problems
in each of the AccessibilitY Analysis areas are provided.
Integration Analysis shows how users have to switch between systems to Complete
a job. These switches can cause usability problems if they are lengthy. Goal Analysis
is concerned with individual systems. Goal Hierarchies are used to show usability
problems in this area. The User Goal Hierarchy represents the sequence of mental
goals a user will need to fulfil in order to complete the task. The System Goal
Hierarchy represents the sequence of goals forced onto the user by the system. Any
mismatches between these hierarchies can cause usability problems. Interaction Analysis
provides a measure of the overall usability of a system. The analysis is based on
guidelines found in the literature. The guidelines are divided into 14 categories.
For each category an applicability and rating is obtained. The applicability is
a measure of how well a system is using the usability features available in the
category. The rating is a measure of how many of the applicable guidelines are satisfied
in the category. Interaction Analysis diagrams show the applicability and rating
for each category. For single systems the diagrams show specific categories with
usability problems. When several diagrams are compared, usability problems across
systems can be seen.
Based on these analyses, the usability of computer systems can be assessed Without
excessive detail before implementation.
|