Architectures

Referring to the prior work about the management of spatio-temporal data in spatio- temporal databases (STDB), there are various concepts which address parts of the dis- cussed issues. A diversified overview of spatial-temporal databases based on different spatio-temporal data models is available in [Abraham and Roddick, 1999] and [Pelekis et al., 2004].

This thesis focuses on spatio-temporal DBMS for managing d-simplicial complexes, which change over time, cf. Section 2.3.1. There are different ways to manage these snapshots while avoiding the storage of redundant information. One popular approach is the use of a differential mode to calculate a specific time step with the help of deltas and an initial model [Abraham and Roddick, 1999]. This idea will be picked up again in Chapter 3.5.

Schäben et al. developed an approach for a spatio-temporal DBMS that is based on the object-relational geodatabase PostGIS14 _{[Le et al., 2013], [Le et al., 2014], [Le, 2014], [Ga-}

briel et al., 2015]. This approach is capable of handling spatio-temporal data based on the snapshot model and is highly related to the 3D modelling software GOCAD.

The geodatabase architecture DB4GeO is realized as an object-oriented approach [Thom- sen et al., 2008], [Breunig et al., 2010]. Both approaches focus mainly on the management of 3D models, but also manage the composition and storage of simple 4D models. Object-oriented approach

The focus on an object-based spatial data model, compared to field-based, is not neces- sarily preceded by an object-oriented implementation. However, [Worboys, 1994b] notes that for the management of spatial data the object-oriented approach is superior to the relational or object-relational approach. This is i.a. due to the complex and widely rami- fied structure of spatio-temporal data [Shekhar et al., 1997].

Among others, [Worboys, 1992] describes the advantages of the object-oriented ap- proach in the context of simplicial complexes. Breunig compares relational with object- oriented databases in the context of mapping spatio-temporal data. As well as Worboys he comes to the conclusion that object-oriented DBMS are superior to relational DBMS, which is particularly related to the following properties [Breunig, 2001]:

 The ability to model spatial and non-spatial data within a unified data model.  1:1 mapping between database types and user-defined data types.

 Representation of the objects behaviour.  Inheritance.

 Polymorphism.

Pelekis supplemented this assessment and points out the following advantages of an ob- ject-oriented approach [Pelekis et al., 2004]:

 A single object represents the entire history of an entity.  Simple queries.

 Efficient temporal data handling.

 Uniform treatment of spatial and temporal data.

14 _{PostGIS – an open source geodatabase, based on the object-relational DBMS Post-}

31 DB4GeO

DB4GeO [Breunig et al., 2009], [Breunig et al., 2010] has its roots in GeoStore, an infor- mation system for managing geologically defined geometries [Alms et al., 1998], [Bode et al., 1994], and in GeoToolKit [Balovnev et al., 2004] which were both developed at the University of Bonn within the scope of the Collaborative Research Center 350 [SFB350]. The primary focus of the development is on the management of spatial data, which is based on simplicial complexes. From the very beginning there was a strong focus on the communication with geological and geophysical 3D modelling tools [Breunig et al., 2000] such as GOCAD or IGMAS [Götze and Lahmeyer, 1988], [Schmidt and Götze, 1998]. The models that were handled by GeoStore and GeoToolKit mainly represented the structure of the Lower Rhine Basin [Alms et al., 1998].

While the two predecessors GeoStore and GeoToolKit were developed in the program- ming language C and C++, DB4GeO has been completely developed in Java. A historical overview of the development of DB4GeO is shown in Table 3.

Table 3 - Historical overview of DB4GeO Time of development Name of the Software Programming Language Innovation

1994 GeoStore C First approach of a 3D geodatabase based on a relational DBMS.

1997 GeoToolKit

and GeoStore

C++ Upgrade to a self-developed object-ori- ented solution: GeoToolKit library 1997 GeoToolKit C++ First spatio-temporal data model 1999 GeoToolKit C++ Extension by a Delta Storage concept.

2002 DB3D Java Re-implementation of the geodatabase

in Java.

2005 DB3D Java Implementation of a spatio-temporal

data model based on ST-simplices.

2007 DB4GeO Java Exchange of the database kernel from

ObjectStore to db4o. First REST-based Web services.

2010 DB4GeO Java Implementation of a spatio-temporal data model for 2-simplicial complexes based on Point Tubes.

The structure of the spatio-temporal database architecture is presented in [Breunig et al., 2010]. It was developed by the use of multiple layers, which depend on each other and

fulfil different tasks. An overview of the structure of the 3D/4D geodatabase architecture DB4GeO is shown in Figure 15.

Figure 15 – Structure of the 3D/4D geodatabase architecture DB4GeO. Source: [Breunig et al., 2009]

The object-oriented DBMS db4o [Paterson et al., 2006]handles the persistent data and forms the basis of DB4GeO. On this, a geometry library was built which provides basic 3D geometries. Here the model of d-simplicial complexes is supported. There are spatial ac- cess structures available, e.g. the R*-Tree [Beckmann et al., 1990] for an accelerated ac- cess to the spatial data. Furthermore, DB4GeO provides an object management, spatial operations, as well as a version management. Spatial data can be queried via a service infrastructure [Breunig et al., 2013b].

[Rolfs, 2005] developed a 4D model to add a support for spatio-temporal data. This model provides the ability to manage time series that consist of simplicial complexes. The devel- opment was a first attempt to handle 4D objects in DB4GeO. Therefore, the model lacks some important features and has the following drawbacks:

 Once inserted a time series cannot be extended.

 The topology of a 4D object cannot change between consecutive time steps.  The vertices of an object are stored redundantly at every net element.

33  The temporal discretization of a 4D object must be uniform within the entire net. The 3D kernel of DB4GeO provides a good basis for an implementation of the of spatio- temporal data management model that is part of the outcome of this thesis.

Additional functionality (spatio-temporal operations and access methods)

The management of spatio-temporal data in a spatio-temporal database does not stop at the pure mapping and storing of the geometry itself. So there are other tasks such as the construction of spatial and spatio-temporal indices, providing spatio-temporal operations or visualization, which must be met by a spatio-temporal DBMS [Abraham and Roddick, 1999].

Especially, the development of various spatial access methods (SAM) and spatio-temporal access methods (STAM) represents an important component of a spatio-temporal DBMS, as they accelerate the access to the data significantly. A good entry point to this research field also for multiple time dimensions can be found in [Menninghaus et al., 2016].