Network Constrained Moving Objects

Foundation

The spatio-temporal database community searches for data models that enable the user to save storage space and speedup query execution on the stored data. One idea in this field is that many moving objects, for example cars and trains, are restricted in their movement by existing networks, like streets and railway networks. In the past, several network data models have been published, which use the knowledge about the existing network and the restriction of the movement of moving objects to this network to save storage space and speedup query execution.

One of these network data models has been presented in [1]. It defines the network dependent spatial and temporal data types corresponding to the spatial and spatio-temporal data types already used in Secondo.

Network Data Model in Secondo

A detailed explanation of the data types and operations mentioned in this section can be found in the Network Guide. The scripts described in this guide are available for download.

A first partial implementation of the network model presented in [1] is part of Secondo since release 2.8.4. It consists of two algebra modules:

• The NetworkAlgebra contains the network object data type (network) itself, the static network constrained data types gpoint (single position), gpoints (set of single positions) and gline (network part), and the operations dealing with these static data types.
• The TemporalNetAlgebra contains the network constrained temporal data types mgpoint, ugpoint and igpoint, and the operations dealing with these data types.

A second improved implementation of [1] is part of Secondo since release 3.3.1. It consists of the algebra module JNetAlgebra, which includes the jnetwork object itself, the static network constrained data types jpoint, jpoints and jline, the moving network constrained data types mjpoint, ujpoint and ijpoint, and the operations dealing with these data types.

Not all algebra modules mentioned in this Section are activated by default in Secondo. The user must remove the # at the start of the lines containing the algebra names in the file makefile.algebras in the Secondo main directory and recompile Secondo to make the data types and operations available.

Other Helpful Algebra Modules in the Network Context

Secondo release 3.3.0 contains two other algebra modules, which are helpful in the context of network operations.

• The OSMAlgebra enables the user to import data files provided by the OpenStreetMap Foundation into Secondo.
• The MapMatchingAlgebra enables the user to import data sets collected by GPS-Devices into Secondo and map them into network constrained moving objects.