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Introduction to GIS Lecture 6 Important Database Concepts Lecture slides by Austin Troy, University of Vermont, © 2007 ©2007 by Austin Troy. All rights reserved Introduction to GIS How is Data Stored? •People use number system with base 10 •Each digit corresponds to 10 to some power •Why are computer values so often in multiples of eight? •A byte is 8 “on-off switches” or bits •Each switch/bit represents a binary number; one byte is 28 or 256 possibilities ©2007 by Austin Troy. All rights reserved Introduction to GIS How do binary numbers translate to real numbers? •Switch combinations determine base ten number based on the formula: •N10= 2b-1+2b-2+…2b-b •Where b= number of bits storing the number •Hence the binary number 11111111 = 27*1+ 26 *1 + 25 *1 + 24 *1 + 23 *1 + 22 *1 + 21 *1 + 20 *1 = 255 •And the binary number 11111110 = 27*1+ 26 *1 + 25 *1 + 24 *1 + 23 *1 + 22 *1 + 21 *1 + 20 *0 = 254 2 10 2 10 ©2007 by Austin Troy. All rights reserved Introduction to GIS Number of Possible Values is fn of number of bits •Number of possible values for a unit of data is an exponential function of the number of switches •28=256 eight bit data •216=65,536 sixteen bit data •232= 4,294,967,296 thirty two bit data ©2007 by Austin Troy. All rights reserved Introduction to GIS Number of bits determines data types Examples of Integer data types Byte: 28 (0 to 255) Short Integer: 216 (ranges from –32,767 to +32,767 without decimals, the sixteenth bit determines sign) Long Integer: 232 (+/-2.147483e+09 ) Floating point: precision can go to either side of decimal place Single precision: 32 bit Double precision: 64 bit ©2007 by Austin Troy. All rights reserved Introduction to GIS Other Data Types Currency Date (recognizes order in dates) String (text) When numbers are represented as text they have no numerical properties (e.g. zip codes) Boolean (yes, no) Object ©2007 by Austin Troy. All rights reserved Introduction to GIS Three Classic Database Models • Hierarchical • Network • Relational -Arc View and Arc Info use this model ©2007 by Austin Troy. All rights reserved Introduction to GIS Hierarchical Database Model A one-to-many method for storing data in a database that looks like a family tree with one root and a number of branches or subdivisions. Problem: linkages in the tables must be known before Groovy 70s TV Action shows Dukes of Hazzard Tom Wopat Eric Estrada CHIPs Larry Wilcox Sitcoms Drama Dallas Larry Hagman Fantasy Island Ricardo Montalban ©2007 by Austin Troy. All rights reserved Starsky and Hutch Love Boat Gavin McLeod Ted Lange David Soul Introduction to GIS Hierarchical Database Model •Example where this model works well: •plant and animal taxonomies •Soil classification •Works when: classes are totally mutually exclusive/ exhaustive •Problem with this model: •Does not work when have entities that belong to several classes or do not have mutual exclusivity •Think about the problems with Windows Explorer •Example: classifying your music collection ©2007 by Austin Troy. All rights reserved Introduction to GIS Networked Database Model A database design for storing information by linking all records that are related with a list of “pointers.” Problem: linkages in the tables must be known before. Not adaptable to change. Action shows Dukes of Hazzard CHIPs NBC Sitcoms Drama Dallas CBS Love Boat Fantasy Island ABC ©2007 by Austin Troy. All rights reserved Three’s company Introduction to GIS Relational (Tabular) Database Model A design used in database systems in which relationships are created between one or more flat files or tables based on the idea that each pair of tables has a field in common, or “key”. In a relational database, the records are generally different in each table The advantages: each table can be prepared and maintained separately, tables can remain separate until a query requires connecting, or relating them, relationships can be one to one, one to many or many to one ©2007 by Austin Troy. All rights reserved Introduction to GIS Data Tables (flat files) Records are the unit that the data are specific to fields Fields, or columns, are attribute categories Cells are where individual values of a record for a field are stored Headings: are the labels for the columns records cells Name Phone Address Student ID *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ©2007 by Austin Troy. All rights reserved Introduction to GIS Data key Is a field that is common to two or more flat files; allows a query to be done across multiple tables or allows two tables to be joined Flat file: professor info Name Phone Address faculty ID *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Flat file: course info Course name Course number enrollment faculty ID *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ©2007 by Austin Troy. All rights reserved Introduction to GIS Join Tables Based on the values of a field that can be found in both tables The name of the field does not have to be the same The data type has to be the same In this case we have a one to Key A B one join; here 1 Key C 1 4 the key is unique 2 5 1 10 2 Key A B C 2 20 3 1 3 6 1 4 10 3 50 2 5 10 2 JOIN ©2007 by Austin Troy. All rights reserved 3 3 6 50 Introduction to GIS Join Tables Key 1 A B 4 1 1 2 2 3 In this case we have a one to many join; here the key is not unique Key C 5 1 2 6 10 20 JOIN ©2007 by Austin Troy. All rights reserved Key 1 A B C 4 10 1 1 2 5 10 2 3 6 20 Introduction to GIS Relational (Tabular) Database Model: 70s TV example Now we can have various flat files (tables) with different record types and with various attributes specific to each record Table 1- specific to actors Actor Year born* Sideburn length David Soul 1948 serious Eric Estrada 1949 moderate Larry Wilcox 1953 slight Starsky David and Hutch Soul Tom Wopat 1950 major CHIPs Eric Larry Wilcox CBS Estrada Dukes Tom Wopat Show Table 2- specific to shows Lead actor Co-star Network * Paul Michael Glaser ABC John Schneider *entirely guessed at- I am not responsible for mistaken TV trivia ©2007 by Austin Troy. All rights reserved NBC Introduction to GIS Relational (Tabular) Database Model This allows queries that go across tables, like which CBS lead actors were born before 1951? Answer: Tom Wopat and David Sole Actor Year born* Sideburn length David Sole 1948 serious Eric Estrada 1949 moderate Larry Wilcox 1953 slight Starsky David and Hutch Soul Tom Wopat 1950 major CHIPs Eric Larry Wilcox ABC Estrada Dukes Tom Wopat It does this by combining information from the two tables, using common key fields Show Lead actor Co-star Network * Paul Michael Glaser CBS John Schneider *entirely guessed at- I am not responsible for mistaken TV trivia ©2007 by Austin Troy. All rights reserved CBS Introduction to GIS Relational (Tabular) Database Model Object-relational databases can contain other objects as well, like images, video clips, executable files, sounds, links Actor Year born* Sideburn length David Soul 1948 serious Eric Estrada 1949 moderate Larry Wilcox 1953 slight Tom Wopat 1950 major Picture ©2007 by Austin Troy. All rights reserved Introduction to GIS Relational Database: another example: property lot info Parcel Street ID address zoning 11 15 Maple St. Residential-1 12 85 Brooks Ave Commercial-2 13 74 Windam Ct. Residential 4 One-to-one relationship Owner Parcel ID occupation J. Smith 13 lawyer R. Jones 11 dentist T. Flores 12 Real estate developer ©2007 by Austin Troy. All rights reserved Introduction to GIS Relational database: one to many relationship Parcel Street ID address zoning 11 15 Maple St. Residential-1 12 85 Brooks Ave Commercial-2 74 Windam Ct. Residential 4 13 In this case, several people co-own the same lot, so no longer one lot, one person One-to-many relationship Owner Parcel ID occupation J. Smith 13 lawyer R. Jones 11 dentist 12 J. McCann financier T. Flores 12 ©2007 by Austin Troy. All rights reserved Real estate developer Introduction to GIS Parcel ID Assuming each owner owned several parcels, we would structure the database differently One-to-many relationship Street zoning address Properties owned by T. Flores 11 15 Maple St. Residential-1 12 85 Brooks Ave Commercial-2 13 74 Windam Ct. Residential 4 Owner occupation # properties owned J. Smith lawyer 2 R. Jones dentist 5 J. McCann financier T. Flores Real estate developer Owner Parcel Date of transaction ID Flores 13 4-15-00 Flores 15 4-17-01 Flores 19 3-12-99 2 3 ©2007 by Austin Troy. All rights reserved Note: this table includes data pertinent only to Flores’ ownership of these properties Introduction to GIS Example Here’s an example of a chart showing the relationships between flat files in a sample relational database for food suppliers* in Microsoft Access * This comes from an MS ACCESS sample database ©2007 by Austin Troy. All rights reserved Introduction to GIS * This comes from an MS ACCESS sample database ©2007 by Austin Troy. All rights reserved Introduction to GIS A real time RDBMS allows for realtime linking and embedding of tables based on common fields Here we see all the orders for product ID 3; there is no need to include product ID in that subtable * This comes from an MS ACCESS sample database ©2007 by Austin Troy. All rights reserved