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Spatial and Temporal Data and Mobility - Coggle Diagram
Spatial and Temporal Data and
Mobility
Motivation
Temporal data
database systems model the current state of the world
Spatial data
Spatial data include geographic data and computer-aided-design data
Multimedia data
The main feature of video and audio data is that the display of the data requires retrieval at a steady, predetermined rate
Mobile databases
Such computers may need to be able to operate while
disconnected from the network
They require special techniques for memory management due to their memory.
Spatial and Geographic Data
Representation of Geometric Information
Geometric information can be represented in different ways
line segment can be represented by the coordinates of its endpoints
Polyline is represented by a list containing the coordinates of the endpoints of the segments, in sequence.
We can represent a polygon by listing its vertices in order
a polygon can be divided into a set of triangles (Triangulation)
Design Databases
Computer-aided-design systems traditionally stored data in memory during editing and wrote the data back to a file at the end of a session of editing.
The objects stored in a design database are generally geometric objects
Three-dimensional surfaces may also be represented by
wireframe models
Design databases also store nonspatial information about objects, like the material from which the objects are constructed
Geographic Data
Applications of Geographic Data
uses
vehicle-navigation systems
distribution-network information
electric-power systems
water-supply systems
land-usage information
Can be categorized in
Vector data
basic geometric objects, like points, line segments, polylines, triangles, and other polygons
Map data are often represented in vector format. Roads are often represented as polylines
Raster data
bit maps or pixel maps, in two or more dimensions. And is often represented as tiles
Geographic information systems usually contain both raster and vector data
Spatial Queries
Nearness queries
request objects that lie near a specified location
Region queries
deal with spatial regions. Such a query can ask for objects
that lie partially or fully inside a specified region
Indexing of Spatial Data
k-d Trees
Each level of a k-d tree partitions the space into two
The k-d-B tree extends the k-d tree to allow multiple child nodes for each internal node, just as a B-tree extends a binary tree, to reduce the height of the tree
Quadtrees
We can use region quadtrees to store array (raster) information.
Each node in the region quadtree
corresponds to a subarray of values.
R-Trees
useful for indexing of objects such as points, line segments, rectangles, and other polygons
A rectangular bounding box is associated with each tree node.
Multimedia Database
Multimedia Data Formats
Because of the large number of bytes required to represent multimedia data, it is essential that multimedia data be stored and transmitted in compressed form.
Some formats are
Image - JPEG
Audio - MPEG-1/2
Video - MP3
Continuous-Media Data
Continuous-media systems are characterized by
their real-time information-delivery requirements
To supply data predictably at the right time to a large number of consumers of the data, the fetching of data from disk must be coordinated carefully
The basic architecture of a video-on-demand
system comprises:
Terminals
People view multimedia data through various devices, collectively referred to as terminals
Network
Transmission of multimedia data from a server to multiple terminals requires a high-capacity network.
Video server
Multimedia data are stored on several disks
Similarity-Based Retrieval
Handwritten data
Handwritten input can be used to identify a handwritten
data item or command stored in the database
Audio data
Speech-based user interfaces are being developed that allow the
user to give a command or identify a data item by speaking.
Pictorial data
databases may store trademark designs, when a new trademark is to be registered, the system may need first to identify all similar trademarks that were registered previously
Mobility and Personal Databases
A Model of Mobile Computing
The mobile-computing environment consists of mobile computers, referred to as mobile hosts, and a wired network of computers.
WAP-based browsers access special Web pages that use wireless markup language, an XML-based language designed for the constraints of mobile and wireless Web browsing.
Mobile hosts communicate with the wired network via computers referred to as mobile support stations
Routing and Query Processing
The route between a pair of hosts may change over time if one of the two hosts is mobile
Mobility results in dynamically changing communication costs, thus complicating the optimization process
Notions of cost to consider:
user time
connection time
time-of-day-based-charges
energy
Broadcast Data
A typical application of broadcast data is stock-market price
information
Reasons to use it:
the mobile host avoids the energy cost for transmitting data requests.
the broadcast data can be received by a large number of mobile hosts at once, at no extra cost.
A mobile host can then receive data as they are transmitted, rather than consuming energy by transmitting a request.
the broadcast medium can be modeled as a disk with a high latency
Disconnectivity and Consistency
Recoverability
Updates entered on a disconnected machine may be lost
if the mobile host experiences a catastrophic failure
Consistency
Locally cached data may become out-of-date, but the mobile
host cannot discover this situation until it is reconnected.
The version-vector scheme detects inconsistencies when copies of a document are independently updated.
Time in Databases
Time Specification in SQL
defines the types date, time, and timestamp
The type time contains two digits for the hour, two digits for the minute, and two digits for the second, and optional fractional digits
The Universal Coordinated Time (UTC) is a standard reference point for specifying time.
SQL supports a type called interval that allows us to refer to a period of time
Temporal Query Languages
snapshot relation
A db relation without temporal information
temporal selection
A selection that involves the time attributes;
temporal projection
projection where the tuples in the projection inherit their times
from the tuples in the original relation
temporal join
A join, with the time of a tuple in the result being the intersection of the times of the tuples from which it is derived.
we must distinguish between time as measured by the system and time as observed in the real world.