Database standards and Modelling Flashcards
What are spatial data standards?
Standards, as defined by the International Organization for Standardization (ISO), are:
◦ “documented agreements containing technical specifications or other precise criteria to be used
consistently as rules, guidelines, or definitions of characteristics,to ensure that materials, products,
procedures, and services are fit for their purpose.”
Spatial data standards facilitate
◦ Data sharing, fitness and suitability of use
◦ Interoperability, interchange and exchange
◦ Openness, access and discovery
Numerous international and national standards organizations have addressed geographic
information.
The Open Geospatial Consortium (OGC) is important in the world of spatial data standards…
Why are there GIS standards?
“International Standards make things work. They give world-class specifications for products, services and systems, to ensure quality, safety and efficiency. They are instrumental in facilitating international trade” (ISO 2018).
“Standards facilitate development, sharing, and use of geospatial data and services” (FGDC
2018).
It is important to consider standards when designing a spatial database.
Open Geospatial Consortium
an international not for profit organization
committed to making quality open standards for the global geospatial community.
These standards are made through a consensus process and are freely available for anyone to use to
improve sharing of the world’s geospatial data.
OGC Standards cover more than just spatial data, they cover data processing, policy and service level
agreements for example.
Key standards include ◦ Simple Features Specification ◦ Simple Features SQL ◦ Keyhole Markup Language (KML) ◦ Geography Markup Language (GML); CityGML ◦ Location Services (OpenLS) ◦ Web Feature Service (WFS); Web Mapping Service (WMS) ◦ Coordinate Transformation
OGC standards are dynamic and consensus driven, responding to the geospatial community nee
International Standards Organization
International Standards Organization (ISO)
◦ ISO is an independent, non-governmental international organization with a membership of 161 national
standards bodies.
◦ Through its members, it brings together experts to share knowledge and develop voluntary, consensus-based,
market relevant International Standards that support innovation and provide solutions to global challenges.
◦ ISO/TC 211 – Geographic Information/Geomatics
American National Standards Institute (ANS
◦ Mission
◦ To enhance both the global competitiveness of U.S.
business and the U.S. quality of life by promoting and
facilitating voluntary consensus
standards and conformity assessment systems, and
safeguarding their integrity.
◦ ANSI accredits more than 200 US standards developers, covering more than 10,000 standards
Geographic Information Modelling Approach of ISO/TC 211 and UML
Geographic Information Modelling Approach of ISO/TC 211
Described by three standards:
◦ ISO 19101 Geographic information – Reference model [1.1]
◦ ISO/TS 19103 Geographic information – Conceptual schema language [1.2]
◦ ISO 19109 Geographic information – Rules for application schema [1.3]
Conceptual Modelling of Systems under ISO/TC 211
◦ Object: Represents an entity in the real world
◦ Class: A set of objects with the same specifications, features, and constraints
◦ Association: Represents connections between classes and objects (instances of those classes)
◦ Generalization: Relationship between a general element and a specific element
UML elements (a very brief introduction)
The Unified Modelling Language (UML) is a graphical language for specifying, constructing, and
documenting systems.
Class
◦ Template for creating new objects
◦ Define properties (attributes) and methods (operations)
◦ e.g. property parcels
Object
◦ Instantiation of a class
◦ Specific instance an object of a given class
◦ e.g. parcel located at 200 University Ave. W
Generalization
◦ Relationship between a more
general class and a more specific
class
◦ Specific class contains all elements
of the general class, plus more
◦ Represented with an open arrow
Associations
◦ Relationships between classes
◦ Multiplicities at both ends
◦ Constraint on number of objects that can be associated with another
object
◦ 1 One and only one
◦ 0..1 Zero or one
◦ M..N From M to N (positive integers)
◦ * or 0..* From 0 to any positive integer
◦ 1..* From 1 to any positive integer
Navigability – information in the class (at the arrow) is
accessible to the class at the other end
Composition – class at closed diamond is composed of
instances of the class at the other end (members of
composition cannot exist independently)
Aggregation – class at open diamond is an aggregation of
instances of the class at the other end (members of
aggregation can exist independently)
Metadata - what is it?
Structured data/information about data in a standards -based format
“Data about the data”
The “who, what, when, where, why, and how” of data / of a database.
◦ “The label on a can of soup”, “catalogue entry for a library book.”
A prerequisite for using data generated or managed by others.
Describes an individual datum, a dataset (object -level metadata), or
a collection of datasets (collection-level metadata).
Metadata – why is it important?
The bad old days
◦ Data in a variety of file formats with no metadata (capability not built in)
◦ Uncertainty, wasted time, errors
Metadata facilitates project management
◦ Facilitates data searching, sharing, and evaluation
◦ Provides an inventory of data assets
◦ Helps determine and maintain the value of data
◦ Helps you determine the reliability and currency of data
◦ Facilitates budgeting and planning
◦ Facilitates searches for data
Object-level Metadata (OLM)
Describe the contents of a single dataset.
Used to determine whether a dataset satisfies the user’s
requirements.
Can be expensive to create.
◦ Require a high level of professional expertise.
◦ Part of the metadata can be created automatically.
Should follow a metadata standard
Metadata Standards
◦ Standardized set of elements describing the data
◦ Rules & guidelines for access and use defined
Metadata registry
◦ A repository of metadata standards
◦ International Standards Organization (ISO) could be considered registry
Spatial Metadata standards –two examples
◦ Federal Geographic Data Committee (FGDC) http://www.fgdc.gov/metadata/geospatial-metadata-
standards
◦ Infrastructure for Spatial Information in the European Community (INSPIRE)
http://inspire.jrc.ec.europa.eu/index.cfm/pageid/101
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Object-level Metadata Standards FGDC CSDGM
FGDC: US Federal Geographic Data Committee’s (FGDC) Content
Standards for Digital Geospatial Metadata (CSDGM)
◦ First published in 1993, widely used.
◦ Comprehensive set of properties of a dataset
◦ High cost of determining the full set of metadata.
FGDC collaborates with:
◦ American National Standards Institute’s (ANSI) Technical Committee for Geographic
Information Systems
◦ International Committee for Information Technology Standards (INCITS-L1)
Object-level Metadata Standards ISO Standards
ISO 19115:
◦ Describes the general content of the metadata and relationships between metadata elements.
◦ Does not provide standards on how the metadata records should be built and formatted.
ISO 19139:
◦ Creates an XML schema (= data model) that prescribes the format of the metadata record.
◦ Provides an encoding schema for describing, validating, and exchanging metadata about geographic
datasets, dataset series, individual geographic features, feature attributes, feature types, feature
properties, etc.
◦ Incorporates metadata elements referenced, but not defined, in ISO 19115, such as the entity and
attribute descriptions addressed by ISO 19109 geospatial standard.
◦ National profiles are currently being developed –US profile development concurrent with Canadian
profile development
Object-level Metadata Standards Dublin Core
Minimum set of properties (“light metadata”)
◦ more likely to have a complete set of metadata associated with a dataset.
Not only for geographical datasets.
Datasets have space and time coverage.
Does not specify how resolution, projection and other spatial properties should be defined.
NTDB (National Topographic data base) Accuracy Standards
Specify geometric, cartographic, and attribute accuracy standards
The NTDB is currently divided into two resolution classes.
◦ Territories located in urban or rural areas are generally available at a resolution close to that of
topographic maps at the 1:50 000 scale,
◦ Urban area: Inhabited part of the Canadian landmass with a high population density whose extent is generally corresponding to
that of urban built-up areas (including suburbs) and industrial parks. Only those cities and towns with more than 5 000
inhabitants(2) and a built-up area of at least 2.25 km2.
◦ Rural area: Inhabited part of the Canadian landmass with a low population density and in which there are human or economic
activities such as agriculture, mining, or fishing.
◦ Territories located in isolated areas are available at a resolution of maps at the 1:250 000 scale.
◦ Isolated area: Uninhabited area of the Canadian landmass that corresponds to the parts not covered by the two preceding classes
(urban and rural areas).
Geometric Accuracy
◦ The accuracy of geometric representation data is given by the difference between the position of the geometric representation associated with an entity (the feature on the map) and the real ground
position of the corresponding topographic feature, as measured with respect to the geodetic network.
The NTDB aims at attaining the following classes of accuracy:
◦ Urban area:
◦ A circular map accuracy standard (CMAS) of 10 meters is the accuracy for data in urban areas.
◦ Rural area:
◦ A CMAS of 25 meters is established as the accuracy for data in rural areas.
◦ Isolated area:
◦ A CMAS of 125 meters is established as the accuracy for data in isolated areas.
NTDB (National Topographic data base) Data Quality
Centre for Topographic Information (CTI) ensures that the topographic data in the NTDB respect
the topographic contents of the source material used according to National Topographic Data
Base Standards and Specifications.
◦ Improper attribution of values to any of the descriptive data will result in a classification error.
◦ An object in the source data but not in the data set is an error of omission.
◦ An object in the data set but not in the source data set is an error of commission.
The maximum acceptable proportion of errors of classification, omission, and commission is all
together 5% for a representative sample.
CTI ensures that the spatial structure of data adheres to National Topographic Data Base
Standards and Specifications. NTDB data contains not more than 1% connection errors and 2%
sharing errors.
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