1.
Data model
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A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to properties of the real world entities. For instance, a model may specify that the data element representing a car be composed of a number of other elements which, in turn, represent the color and size of the car. The term data model is used in two distinct but closely related senses, at other times it refers to a set of concepts used in defining such formalizations, for example concepts such as entities, attributes, relations, or tables. So the data model of an application may be defined using the entity-relationship data model. This article uses the term in both senses, a data model explicitly determines the structure of data. Data models are specified in a modeling notation, which is often graphical in form. A data model can sometimes be referred to as a data structure, Data models are often complemented by function models, especially in the context of enterprise models. Managing large quantities of structured and unstructured data is a function of information systems. Data models describe the structure, manipulation and integrity aspects of the data stored in data management systems such as relational databases and they typically do not describe unstructured data, such as word processing documents, email messages, pictures, digital audio, and video. The main aim of data models is to support the development of systems by providing the definition. According to West and Fowler if this is done consistently across systems then compatibility of data can be achieved, if the same data structures are used to store and access data then different applications can share data. The results of this are indicated above, however, systems and interfaces often cost more than they should, to build, operate, and maintain. They may also constrain the business rather than support it, a major cause is that the quality of the data models implemented in systems and interfaces is poor. Business rules, specific to how things are done in a place, are often fixed in the structure of a data model. This means that changes in the way business is conducted lead to large changes in computer systems. Entity types are not identified, or incorrectly identified. This can lead to replication of data, data structure, and functionality, together with the attendant costs of that duplication in development, Data models for different systems are arbitrarily different. The result of this is that complex interfaces are required between systems that share data and these interfaces can account for between 25-70% of the cost of current systems
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Digital elevation model
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A digital elevation model is a digital model or 3D representation of a terrains surface — commonly for a planet, moon, or asteroid — created from terrain elevation data. There is no usage of the terms digital elevation model, digital terrain model. In most cases the term digital surface model represents the earths surface, in contrast to a DSM, the digital terrain model represents the bare ground surface without any objects like plants and buildings. DEM is often used as a term for DSMs and DTMs. Other definitions equalise the terms DEM and DTM, or define the DEM as a subset of the DTM, there are also definitions which equalise the terms DEM and DSM. On the Web definitions can be found which define DEM as a regularly spaced GRID, most of the data providers use the term DEM as a generic term for DSMs and DTMs. All datasets which are captured with satellites, airplanes or other flying platforms are originally DSMs and it is possible to compute a DTM from high resolution DSM datasets with complex algorithms. In the following the term DEM is used as a term for DSMs and DTMs. A DEM can be represented as a raster or as a vector-based triangular irregular network, the TIN DEM dataset is also referred to as a primary DEM, whereas the Raster DEM is referred to as a secondary DEM. The DEM could be acquired through techniques such as photogrammetry, lidar, IfSAR, land surveying, DEMs are commonly built using data collected using remote sensing techniques, but they may also be built from land surveying. DEMs are used often in information systems, and are the most common basis for digitally produced relief maps. Mappers may prepare digital elevation models in a number of ways, the SPOT1 satellite provided the first usable elevation data for a sizeable portion of the planets landmass, using two-pass stereoscopic correlation. The HRS instrument on SPOT5 has acquired over 100 million square kilometers of stereo pairs, older methods of generating DEMs often involve interpolating digital contour maps that may have been produced by direct survey of the land surface. This method is used in mountain areas, where interferometry is not always satisfactory. Note that contour line data or any other sampled elevation datasets are not DEMs, a DEM implies that elevation is available continuously at each location in the study area. The quality of a DEM is a measure of how accurate elevation is at each pixel, the limitation with the GTOPO30 and SRTM datasets is that they cover continental landmasses only, and SRTM does not cover the polar regions and has mountain and desert no data areas. SRTM data, being derived from radar, represents the elevation of the first-reflected surface — quite often tree tops, so, the data are not necessarily representative of the ground surface, but the top of whatever is first encountered by the radar. Submarine elevation data is generated using ship-mounted depth soundings, when land topography and bathymetry is combined, a truly Global Relief Model is obtained
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Open Geospatial Consortium
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The Open Geospatial Consortium, an international voluntary consensus standards organization, originated in 1994. A predecessor organization, OGF, the Open GRASS Foundation, started in 1992, from 1994 to 2004 the organization also used the name Open GIS Consortium. The OGC website gives a history of the OGC. Currently a candidate standard waiting for votes, considerable progress has been made in defining Representational State Transfer web services, e. g. OGC SensorThings API. The OGC has three units, the Specification program the Interoperability Program Outreach and Community Adoption The OGC has a close relationship with ISO/TC211. Volumes from the ISO19100 series under development by this committee progressively replace the OGC abstract specification, further, the OGC standards Web Map Service, GML, Web Feature Service, Observations and Measurements, and Simple Features Access have become ISO standards. The OGC works with more than 20 international standards-bodies including W3C, OASIS, WfMC, and the IETF
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XML
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In computing, Extensible Markup Language is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. The W3Cs XML1.0 Specification and several other related specifications—all of them free open standards—define XML, the design goals of XML emphasize simplicity, generality, and usability across the Internet. It is a data format with strong support via Unicode for different human languages. Although the design of XML focuses on documents, the language is used for the representation of arbitrary data structures such as those used in web services. Several schema systems exist to aid in the definition of XML-based languages, hundreds of document formats using XML syntax have been developed, including RSS, Atom, SOAP, SVG, and XHTML. XML-based formats have become the default for many office-productivity tools, including Microsoft Office, OpenOffice. org and LibreOffice, XML has also provided the base language for communication protocols such as XMPP. Applications for the Microsoft. NET Framework use XML files for configuration, apple has an implementation of a registry based on XML. XML has come into use for the interchange of data over the Internet. IETF RFC7303 gives rules for the construction of Internet Media Types for use when sending XML and it also defines the media types application/xml and text/xml, which say only that the data is in XML, and nothing about its semantics. The use of text/xml has been criticized as a source of encoding problems. RFC7303 also recommends that XML-based languages be given media types ending in +xml, further guidelines for the use of XML in a networked context appear in RFC3470, also known as IETF BCP70, a document covering many aspects of designing and deploying an XML-based language. The material in this section is based on the XML Specification and this is not an exhaustive list of all the constructs that appear in XML, it provides an introduction to the key constructs most often encountered in day-to-day use. Character An XML document is a string of characters, almost every legal Unicode character may appear in an XML document. Processor and application The processor analyzes the markup and passes structured information to an application, the specification places requirements on what an XML processor must do and not do, but the application is outside its scope. The processor is often referred to colloquially as an XML parser, Markup and content The characters making up an XML document are divided into markup and content, which may be distinguished by the application of simple syntactic rules. Generally, strings that constitute markup either begin with the character < and end with a >, or they begin with the character &, strings of characters that are not markup are content. However, in a CDATA section, the delimiters <. > are classified as markup, in addition, whitespace before and after the outermost element is classified as markup. Tag A tag is a construct that begins with <
5.
Shapefile
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The shapefile format is a popular geospatial vector data format for geographic information system software. It is developed and regulated by Esri as a specification for data interoperability among Esri. The shapefile format can spatially describe vector features, points, lines, and polygons, representing, for example, water wells, rivers, each item usually has attributes that describe it, such as name or temperature. The shapefile format is a vector storage format for storing geometric location. This format lacks the capacity to store topological information, the shapefile format was introduced with ArcView GIS version 2 in the early 1990s. It is now possible to read and write geographical datasets using the format with a wide variety of software. The shapefile format is simple because it can store the primitive data types of points, lines. Shapes together with data attributes can create infinitely many representations about geographic data, representation provides the ability for powerful and accurate computations. The term shapefile is quite common, but is misleading since the format consists of a collection of files with a common filename prefix, the three mandatory files have filename extensions. shp. shx, and. dbf. The actual shapefile relates specifically to the. shp file, the. shp and. shx files have various fields with different endianness, so an implementer of the file formats must be very careful to respect the endianness of each field and treat it properly. The main file contains the geometry data, the binary file consists of a single fixed-length header followed by one or more variable-length records. Each of the variable-length records includes a component and a record-contents component. A detailed description of the format is given in the ESRI Shapefile Technical Description. This format should not be confused with the AutoCAD shape font source format, the 2D axis ordering of coordinate data assumes a Cartesian coordinate system, using the order or. This axis order is consistent for Geographic coordinate systems, where the order is similarly, geometries may also support 3- or 4-dimensional Z and M coordinates, for elevation and measure, respectively. A Z-dimension stores the elevation of each coordinate in 3D space, the user-defined M dimension can be used for one of many functions, such as storing linear referencing measures or relative time of a feature in 4D space. The following are the possible types, The index contains the same 100-byte header as the. shp file. It is also possible to seek forwards an arbitrary number of records using the same method, attributes for each shape are stored in dBase format
