Skip to search form Skip to main content. Aldaijy Published Abstract : Geographic information systems GIS provide timely and precise spatial information for command and control systems. GIS support decision makers in formulating plans and making critical decisions in preparedness, response, recovery, and mitigation phase of crisis management. View PDF. Save to Library. Create Alert. Share This Paper. Figures and Tables from this paper. Figures and Tables. A multidimensional Bernoulli spatial scan statistics method is developed to detect OD region pairs with abnormally high concentrations of one movement dataset over the other.
The existence and the spatial extents of these OD region pairs indicate whether and where the two movement distributions differ.
Multidimensional Geographic Information Science
Two case studies were conducted to evaluate the approach by comparing morning and afternoon taxi trips individual movements , and county-to-county migration flows between age groups aggregated movement flows , and demonstrated that areas with the most significant spatial distribution differences could be detected from large movement datasets.
A multidimensional spatial scan statistics approach to movement pattern comparison. N2 - This paper describes a multidimensional spatial scan statistics approach to comparing spatial movement patterns based on origin—destination OD representation. AB - This paper describes a multidimensional spatial scan statistics approach to comparing spatial movement patterns based on origin—destination OD representation. H defines a set of hypercube tags;.
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M defines a set of measures for a fact;. I j defines relationships between dimensions and domains. N p defines relationships between domains and members. As the definition of XLink allows types of relationships between elements, by the use of the attribute xlink:arcrole, this is used for the definition, considered below, of relationships between elements representing members, domains, dimensions, facts and cubes. Figure 2 shows how the relationships defined by the Definition 6 can be established. Each circle represents a node, which corresponds to an XML element. The lines that connect the nodes represent the possible relationship types that can exist between the elements.
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The domain-member relationship connects elements that are part of a domain. The dimension-domain relationship links the domain to the dimension. The hypercube-dimension relationship connects the fact to the dimension. Lastly, the relationships all and not-all state, for a given fact, whether all domain members are part of the hypercube or not. These relationships are established in the XLDM metamodel through link bases. The XML formalism allows the insertion of sub-elements multi-levels in an XML element and the establishment of relationships, through XLink, which define hierarchies among elements.
Thus, the definition of the domain-member relationship allows the building of hierarchies in a dimension. For example, one dimension country can have a domain-member relationship with the element brazil, then, this one can have the same kind of relationship with other elements, e. Based on the definitions discussed in this section, documents that compose the XLDM metamodel specification were created. Next, the XLDM document specifications are discussed. It is noticed that, due to the inherent XML technology flexibility, different data cube metamodels for data warehouses based on XML can be specified.
For this reason, XML data heterogeneity problems are made evident. However, the use of XLink and XML Schema can solve such problems through the specification of dimensions, facts and cubes. The proposed multidimensional metamodel is based on the definitions presented in section 3. To do so, instance-schema. The schemas specify the elements that represent the facts, the dimensions, the dimension members and the cubes.
The linkbases define the relationships between members, dimensions and facts, establishing combinations of cubes that can exist. In the instance, the facts occur and, combined with dimension members, determine a data cube. The XML instance document, which may contain one or more cubes, has a structural dimensionin which the contexts are presented with the dimension members.
There is also a non-dimensional structure, with the measures of the facts. This figure illustrates the data organization according to this model. Based on XML Schema, the vocabulary, i. The relationships among the instance elements and between them and other resources are expressed in linkbases. The specified data types are common to a variety of domains. This was done in order to broaden the model applicability. However, it is possible to create types for a specific domain.
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The attributes and elements declarations, which can be found in XLDM instances, are made in instance-schema. An element declaration of particular importance, the instance root element, is shown in Listing 1. The presence of this element and its children in the instance is based on Definition 1, 2 and 3. Initially, the element naming is performed. In XLDM, two alternatives are given to this element identification, in order to name it according to the domain to which it is being applied: 1 changing its declaration in the instance-schema.
Thus, the instance xldm element has a label, for domain application, specified on the link base label. Next, there is the element description. After this, the declarations of the references to schemas, link bases, roles and arcroles are performed. A significant characteristic is the obligatoriness of two link bases entitled Definition and Label, which will be discussed later.
Thus, the number of minimum occurrences in the linkbaseRef element is defined as two. Finally, the elements that can occur in the instance are declared, such as item and tuple. Fact Schema and Hypercube Schema are created from the instance-schema.
Regarding organization purposes, these schemas can be specified in the same document or in distinct documents. In the instance documents, it is mandatory the presence of contextRef and unitRefattributes in the elements that represent the facts. They make reference to the dimensional context and the fact unit, represented by the elements context and unit, found in the multidimensional structure. Linkbases are defined to conform to the relationships that can be present in a great variety of domains.
The definitions occur by adding roles specification for the arcrole attribute, besides the inclusion of elements and attributes.
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Listing 2 shows the arcrole multiplication-item specification and, in Listing 3 , the Description linkbase definitionis illustrated. XLDM proposed linkbases willbe discussed next and their uses are illustrated in Section 4. The Definition linkbase, considered mandatory, allows the creation of the hierarchical element structure.
This solves the problem of structural heterogeneity. For the structural aspect, the relationship definition among dimensions, members and cubes is performed by the Definitionlinkbase. The relationship is expressed by the arcrole domain-member lists and the possible members of a domain, which is associated to the dimension through the arcrole dimension-domain. The cross product between the dimensions and the facts, in order to establish the possible cubes to be used in the instance, is defined by the arcrole hypercube-dimension.
To include the measures in the cube, the arcrole all is to be used and to exclude the member of a domain in a cube specification, the arcrolenotAll is also used. These relations, based on the Definitions 5, 6 e 7, determine the relationship among members, dimensions, facts, cubes and possible values for the attribute arcrole, so that a data multidimensional model may be created. These relationships are shown in Figure 2.
Besides these relationships, illustrated in Listing 6 , other relationships are also specified. Their definition occurs with the following arcroles: a main, which defines a relationship between a concept and another as main, e. In the disease treatment example, there may be the main procedure and the secondary ones. Then, the attribute order indicates the order in which the secondary procedures should be performed; c substitution, which determines the possibility of substitution of a concept for another one, e.
The attribute order indicates the order in which the concepts can be replaced, e. The Label linkbase allows the use of different labels for the same element, which can be specified in different languages through the attribute xml:lang. This is mandatory, so that the semantic and syntactic heterogeneities can be avoided;. The Ordering linkbase is an optional linkbase defined to determine not only the elements' presentation order in the instance, but also their processing order, which can differ from the presentation. For the definition of links aiming at specifying the presentation orders, an extended link element presentationLink is used.
For processing purposes, the element processingLink is used;. The Description linkbase is another optional linkbase introduced in this metamodel in order to supply textual description to a relationship. For example, the relationship between a disease and its description is represented by these linkbase arcs. Placing the descriptions in a different linkbase contributes to the model modularity;.
The Reference linkbase is also optional and it is used to define elements that represent references;. The Calculation linkbase expresses arithmetic relations. It was defined so that, besides the sum operation, the arithmetic operations of multiplication, division, exponentiation and n-th root are specified. To do so, values are defined for the arcrole attribute. Listing 4 shows the possible arcroles for this linkbase, which depends on the arithmetic operation. Attributes are also defined, with proper domains, for each kind of operation.
For example, the attribute weight changes its domain based on the operation.
For sums, the domain varies from -1 to 1, what means that its value is completely or partially used in the addition, which results in the parent element value. This attribute domain for multiplication is the set of real numbers. Regarding the exponentiation and n-th root operations, there are the attributes exponent and index, of which domain is the set of natural numbers.
For division, only the arcrole values are used in the numerator and denominator specification. By using XLDM, the heterogeneity questions of the XML data, mentioned in section 1, are solved as follows: i in semantics, the Label linkbase establishes one or more names for an element defined in the schema.
Therefore, a unique element can have several names, and distinct elements in different domains can have the same name. This allows an application to perform the processing through the element itself or through its label; ii in syntactic, the Label linkbaseallows the definition of names in different languages for the same element and the attribute unit allows to inform the unit referring to the measure; and iii in the structural, the schema defines the elements, their attributes, and child elements.