Repositório Colecção:http://hdl.handle.net/10198/29842014-07-13T15:14:28Z2014-07-13T15:14:28ZD3S - a distributed storage serviceLopes, RuiSernadela, Pedrohttp://hdl.handle.net/10198/96512014-06-17T01:00:53Z2013-01-01T00:00:00ZTítulo: D3S - a distributed storage service
Autor: Lopes, Rui; Sernadela, Pedro
Resumo: The Internet growth allowed an explosion of service provision in the cloud. The cloud paradigm dictates the users` information migration from the desktop into the network allowng access averyhere, anytime. This paradigm provided a adequate environment to the emergency of online storage services, such as Amazon S3. This kind of services allows storing digital data in a transparent way, in a pay-as-you-go model. This paper describes an implementation of an S3 compatible cloud storage service based on peer-to-peer networks, in particular, through the BitTorrent protocol. This approach allows taking advantage of the intrisic features of this kind of networks, in particular possibility for simultaneous downlouading of pieces from different locations and the fault tolerance.2013-01-01T00:00:00ZImplementation of an information technology infrastructure library process – the resistance to changeEsteves, RuiAlves, Paulohttp://hdl.handle.net/10198/96412014-06-06T09:30:46Z2013-01-01T00:00:00ZTítulo: Implementation of an information technology infrastructure library process – the resistance to change
Autor: Esteves, Rui; Alves, Paulo
Resumo: This paper presents the preliminary results of an academic research about implementation of an Information Technology Infrastructure Library (ITIL) process conducted in 2012 in a Portuguese public organization named Culture, Tourism and Transport Regional Department of Madeira Autonomous Region. During the process we encountered resistance against ITIL and adversity to change. It is also true that other factors occurred in this project as the change of economic conditions or constrained resources. With this study we can conclude that ITIL is useful for increasing the overall quality of IT services, reduced costs, improved customer satisfaction, improved productivity and delivery, but we found that particularly in the public sector there is a natural resistance to change. This resistance is the most important issue for the deployment of ITIL practices in public sector because the formal and bureaucratic processes are settled in the culture of organizations.2013-01-01T00:00:00ZAdopting an opensource integrated library system in academic libraries: experiences so far with Koha and RFID at Polytechnic Institute of BragançaAlves, PauloReais, AntónioAlves, Evandrohttp://hdl.handle.net/10198/92602014-02-03T11:07:59Z2012-01-01T00:00:00ZTítulo: Adopting an opensource integrated library system in academic libraries: experiences so far with Koha and RFID at Polytechnic Institute of Bragança
Autor: Alves, Paulo; Reais, António; Alves, Evandro
Resumo: Open source has a major role in several applications in education, government and business. In higher
education the adoption of open source software in Library management is not so common as in virtual
learning environments, content management systems and portals. Even considering the fact that open
source Integrated Library Systems are in the market for a long time, there are several barriers that
libraries are facing when considering the adoption of open source. This paper highlights the advantages
of adopting an open source Library Management System and describes the migration process from a
commercial system to Koha and the integration of RFID for books circulation and user identification.2012-01-01T00:00:00ZAn effective algorithm for obtaining the set of all minimal cost pairs of disjoint paths with dual arc costsGomes, TeresaCraveirinha, JoséJorge, Luísahttp://hdl.handle.net/10198/74982013-09-24T09:53:41Z2008-01-01T00:00:00ZTítulo: An effective algorithm for obtaining the set of all minimal cost pairs of disjoint paths with dual arc costs
Autor: Gomes, Teresa; Craveirinha, José; Jorge, Luísa
Resumo: In today’s telecommunications networks it is necessary, for reliability reasons, to use protection schemes involving the calculation of two (or more) disjoint paths for each node-to-node connection, especially when large amounts of traffic have to be routed in the network. This concern is
particularly relevant in optical networks, namely WDM (Wavelength Division Multiplexing) networks due to the very high rates supported by lightpaths, and in the Internet using MPLS (Multiprotocol
Label Switching). In this context the problem of obtaining optimal (arc or node) disjoint paths, for increasing network reliability while minimising bandwidth consumption, is extremely important.
The problem of finding k disjoint paths from s to t (two distinct nodes), in a network with k different costs on every arc such that the total cost of the paths is minimised is NP-complete even for k = 2,
when the relationship between the k arc costs (in the same arc) is arbitrary. When k = 2 these networks are usually designated as dual arc cost networks.
In this paper we propose an exact algorithm for finding the whole set of arc-disjoint path pairs, with minimal cost in a network with dual arc costs. The addressed problem can be formalised as follows.
Let G = (V,E) be a directed network with node set V = {v1, v2, . . . , vn} and and arc set E =
{e1, e2, . . . , em} (were n and m designate the number of nodes and arcs in G, respectively), where
two different non-negative cost functions (or metrics) in the arcs, are defined:
η(j) : E → IN0 (j = 1, 2) (1)
η(j)((va, vb)) = c(j)
vavb (va, vb) ∈ E (2)
The cost C(j) of a (loopless) path p in G with respect to metric η(j), is:
C(j)(p) =
X
(va,vb)∈p
c(j)
vavb (j = 1, 2) (3)
Let path p, p = hv1, e1, v2, . . . , vi−1, ei−1, vii, be given as an alternate sequence of nodes and arcs
from G, such that the tail of ek is vk and the head of ek is vk+1, for k = 1, 2, . . . , i − 1 (all the vi in
p are different). Let the set of nodes in p be V ∗(p) and the set of arcs in p be E∗(p). Two paths
p = hv1, e1, v2, . . . , vi−1, ei−1, vii and q are arc-disjoint if E∗(p) ∩ E∗(q) = ∅. Two paths p and q are
disjoint if V ∗(p) ∩ V ∗(q) = ∅, and are internally disjoint if {v2, . . . , vi−1} ∩ V ∗(q) = ∅. We will say that
two paths are node disjoint if they are internally disjoint.
The addressed problem is to find the whole set of pairs (p, q) of arc disjoint paths which minimise the
total cost of the pair, defined by:
C[(p, q)] = C(1)(p) + C(2)(q) (4)
where p and q have the same source and sink node.
An exact algorithm for solving this NP-complete problem will be proposed, based on a condition which
guarantees that the optimal path pair cost has been obtained. This optimality condition is based on
the calculation of increasingly tightened upper and lower bounds on the optimal cost. A formal proof
of the correctness of the algorithm is described. Extensive experimentation is presented to show the
effectiveness of the algorithm.
It will also be explained how the proposed approach can also be used for obtaining the minimal cost
disjoint path pair with constraints on the maximum number of arcs allowed per path, a problem of interest in various applications, namely in telecommunication networks.2008-01-01T00:00:00Z