DSpace Collection:https://dspace.lboro.ac.uk/2134/22702017-01-21T04:22:33Z2017-01-21T04:22:33ZOn restricting the ambiguity in morphic images of wordsDay, Joel D.https://dspace.lboro.ac.uk/2134/231712016-11-22T14:49:54Z2016-01-01T00:00:00ZTitle: On restricting the ambiguity in morphic images of words
Authors: Day, Joel D.
Abstract: For alphabets Delta_1, Delta_2, a morphism g : Delta_1* to Delta_2* is ambiguous with respect to a word u in Delta_1* if there exists a second morphism h : Delta_1* to Delta_2* such that g(u) = h(u) and g not= h. Otherwise g is unambiguous. Hence unambiguous morphisms are those whose structure is fully preserved in their morphic images.
A concept so far considered in the free monoid, the first part of this thesis considers natural extensions of ambiguity of morphisms to free groups. It is shown that, while the most straightforward generalization of ambiguity to a free monoid results in a trivial situation, that all morphisms are (always) ambiguous, there exist meaningful extensions of (un)ambiguity which are non-trivial - most notably the concepts of (un)ambiguity up to inner automorphism and up to automorphism.
A characterization is given of words in a free group for which there exists an injective morphism which is unambiguous up to inner automorphism in terms of fixed points of morphisms, replicating an existing result for words in the free monoid. A conjecture is presented, which if correct, is sufficient to show an equivalent characterization for unambiguity up to automorphism. A rather counterintuitive statement is also established, that for some words, the only unambiguous (up to automorphism) morphisms are non-injective (or even periodic).
The second part of the thesis addresses words for which all non-periodic morphisms are unambiguous. In the free monoid, these take the form of periodicity forcing words. It is shown using morphisms that there exist ratio-primitive periodicity forcing words over arbitrary alphabets, and furthermore that it is possible to establish large and varied classes in this way. It is observed that the set of periodicity forcing words is spanned by chains of words, where each word is a morphic image of its predecessor. It is shown that the chains terminate in exactly one direction, meaning not all periodicity forcing words may be reached as the (non-trivial) morphic image of another. Such words are called prime periodicity forcing words, and some alternative methods for finding them are given.
The free-group equivalent to periodicity forcing words - a special class of C-test words - is also considered, as well as the ambiguity of terminal-preserving morphisms with respect to words containing terminal symbols, or constants. Moreover, some applications to pattern languages and group pattern languages are discussed.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.2016-01-01T00:00:00ZA blackboard-based system for learning to identify images from feature dataNorman, Margarethttps://dspace.lboro.ac.uk/2134/220132016-07-19T14:03:44Z1991-01-01T00:00:00ZTitle: A blackboard-based system for learning to identify images from feature data
Authors: Norman, Margaret
Abstract: A blackboard-based system which learns recognition rules for
objects from a set of training examples, and then identifies and locates
these objects in test images, is presented. The system is designed to use
data from a feature matcher developed at R.S.R.E. Malvern which finds the
best matches for a set of feature patterns in an image. The feature
patterns are selected to correspond to typical object parts which occur
with relatively consistent spatial relationships and are sufficient to
distinguish the objects to be identified from one another.
The learning element of the system develops two separate sets of
rules, one to identify possible object instances and the other to attach
probabilities to them. The search for possible object instances is
exhaustive; its scale is not great enough for pruning to be necessary.
Separate probabilities are established empirically for all combinations
of features which could represent object instances. As accurate
probabilities cannot be obtained from a set of preselected training
examples, they are updated by feedback from the recognition process.
The incorporation of rule induction and feedback into the blackboard
system is achieved by treating the induced rules as data to be held on a
secondary blackboard. The single recognition knowledge source
effectively contains empty rules which this data can be slotted into,
allowing it to be used to recognise any number of objects - there is no
need to develop a separate knowledge source for each object. Additional
object-specific background information to aid identification can be added
by the user in the form of background checks to be carried out on
candidate objects.
The system has been tested using synthetic data, and successfully
identified combinations of geometric shapes (squares, triangles etc.).
Limited tests on photographs of vehicles travelling along a main road
were also performed successfully.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.1991-01-01T00:00:00ZApplications of the Galois Model LFSR in CryptographyGardner, Davidhttps://dspace.lboro.ac.uk/2134/219322016-07-11T08:34:40Z2016-01-01T00:00:00ZTitle: Applications of the Galois Model LFSR in Cryptography
Authors: Gardner, David
Abstract: The linear feedback shift-register is a widely used tool for generating cryptographic sequences. The properties of the Galois model discussed here offer many opportunities to improve the implementations that already exist. We explore the overall properties of the phases of the Galois model and conjecture a relation with modular Golomb rulers. This conjecture points to an efficient method for constructing non-linear filtering generators which fulfil Golic s design criteria in order to maximise protection against his inversion attack. We also produce a number of methods which can improve the rate of output of sequences by combining particular distinct phases of smaller elementary sequences.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.2016-01-01T00:00:00ZModelling the instrumental value of software requirementsEllis-Braithwaite, Richardhttps://dspace.lboro.ac.uk/2134/218032016-07-20T13:10:02Z2015-01-01T00:00:00ZTitle: Modelling the instrumental value of software requirements
Authors: Ellis-Braithwaite, Richard
Abstract: Numerous studies have concluded that roughly half of all implemented software requirements are never or rarely used in practice, and that failure to realise expected benefits is a major cause of software project failure. This thesis presents an exploration of these concepts, claims, and causes. It evaluates the literature s proposed solutions to them, and then presents a unified framework that covers additional concerns not previously considered.
The value of a requirement is assessed often during the requirements engineering (RE) process, e.g., in requirement prioritisation, release planning, and trade-off analysis. In order to support these activities, and hence to support the decisions that lead to the aforementioned waste, this thesis proposes a framework built on the modelling languages of Goal Oriented Requirements Engineering (GORE), and on the principles of Value Based Software Engineering (VBSE).
The framework guides the elicitation of a requirement s value using philosophy and business theory, and aims to quantitatively model chains of instrumental value that are expected to be generated for a system s stakeholders by a proposed software capability. The framework enriches the description of the individual links comprising these chains with descriptions of probabilistic degrees of causation, non-linear dose-response and utility functions, and credibility and confidence. A software tool to support the framework s implementation is presented, employing novel features such as automated visualisation, and information retrieval and machine learning (recommendation system) techniques. These software capabilities provide more than just usability improvements to the framework. For example, they enable visual comprehension of the implications of what-if? questions, and enable re-use of previous models in order to suggest modifications to a project s requirements set, and reduce uncertainty in its value propositions.
Two case studies in real-world industry contexts are presented, which explore the problem and the viability of the proposed framework for alleviating it. The thesis research questions are answered by various methods, including practitioner surveys, interviews, expert opinion, real-world examples and proofs of concept, as well as less-common methods such as natural language processing analysis of real requirements specifications (e.g., using TF-IDF to measure the proportion of software requirement traceability links that do not describe the requirement s value or problem-to-be-solved).
The thesis found that in general, there is a disconnect between the state of best practice as proposed by the literature, and current industry practice in requirements engineering. The surveyed practitioners supported the notion that the aforementioned value realisation problems do exist in current practice, that they would be treatable by better requirements engineering practice, and that this thesis proposed framework would be useful and usable in projects whose complexity warrants the overhead of requirements modelling (e.g., for projects with many stakeholders, competing desires, or having high costs of deploying incorrect increments of software functionality).
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.2015-01-01T00:00:00Z