chapter 11.pdf

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University of Guelph
Computing and Information Science
CIS 1200
John Saville

1 Chapter 11: Behind the Scenes: Databases and Information Systems Life Without Databases ▯ Database is a collection of related data that can be easily stored, sorted, organized, and queried ▯ A key attribute of databases is that information can be filtered so that you can only see the info you really want (ex. Facebook) Should I use databases for managing all types of data? ▯ NO, simple lists can be created on word processing or spreadsheet software, a spreadsheet in Microsoft excel, or table in Word When is a list not appropriate? ▯ If complex information needs to be organized or more than one needs access to it, a list is not an efficient solution What’s  the  problem  with  having  two  lists? ▯ A great deal of duplicated data between the two lists ▯ Data redundancy is when the same data exists in more than one place in a database ▯ Each time the information in the list changes, multiple lists must be updated (data inconsistency) Aside from data redundancy and inconsistency, are there any other problems with using lists instead of databases? ▯ With a list, anything can be entered in a row or column, even if that information is incorrect ▯ Information can be organized in many ways ▯ How to handle incomplete data Cant I Just exercise caution and set rules for updating lists? ▯ Being careful does not avoid the most pressing problems or lists: 1. Inability of data to be shared 2. Data redundancy How can I solve the problems associated with lists? ▯ Single topics: lists is sufficient ▯ Complex data: a database is sufficient Database Building Blocks Advantages to Databases How do databases make out lives easier? ▯ Allow easy retrieval and storage of large quantities of info ▯ Extremely large electronic databases can provide info in seconds ▯ THREE main ADVANTAGES: 1. Enable info storing 2. Promote data integrity 3. Flexible use of data How do databases make information sharing possible? ▯ One file is maintained, which reduces errors and increases efficiency 2 How do databases promote data integrity? ▯ Data integrity means that the data contained in the database is accurate and reliable ▯ Data centralization is having all your data in one central location. It helps ensure data integrity by requiring data to be updated only by one place if the data changes How do databases provide flexibility? ▯ You can reorganize the info they contain in a variety of ways to suit the needs of the moment ▯ Data flexibility makes info dissemination tasks easier Disadvantages with databases ▯ More complex to construct ▯ Time-consuming, and expensive ▯ Great care must be involved to ensure they will function properly ▯ Database administrator (or database designer) is an individual trained in the design and building of databases, to assist with the construction of large databases ▯ Data privacy Database Terminology How is data stored in a database? ▯ THREE main COMPONENTS: fields, records, and tables What is a field? ▯ Displayed in columns ▯ Each field is identified by a field name which is way of describing the field What are data types? ▯ A data type is assigned when fields are created in a database ▯ There  are  7  different  common  data  types….. 1. Text field holds words 2. Numeric field holds numbers 3. Computational field (computed field) numeric field that stores calculations 4. Data field holds data such as bdays and due dates 5. Memo field holds long pieces of text 6. Object field holds pictures, video clips, or documents 7. Hyperlink field stores hyperlinks to webpages What is meant by a field size? ▯ Is the max number of characters or numbers that a field can hold ▯ If numeric field has a size of 5 it can hold a number as large as 99999 What are records and tables? ▯ A record is a group of related fields ▯ A table is a group of related records Primary Keys Can fields have the same values in the same table? 3 ▯ YES, two students may have the same last name ▯ A primary field or key field is one field that has a value unique to that similar record What makes a good primary key? ▯ Numbers Database Types 1. Relational 2. Object-oriented 3. Multidimensional 1) Relational Databases What is a relational database? ▯ Organizes data in table format by logically grouping similar data in relation ▯ Tables are logically linked to each other by including their primary keys in other tables with related info Who invented the relational database? ▯ E. F. Codd in 1970 2) Object-Oriented Databases What is an object-oriented database? ▯ Stores data in objects rather than in tables ▯ Objects contain not only data, but also methods for processing or manipulating that data ▯ These databases store more types of data and able access to data faster Why would I use an object-oriented database? ▯ They are more adept at handling unstructured data. Ex, audio clips, video clips, pictures, and extremely large documents ▯ Binary Large Object (BLOB) is known as this data because it is actually encoded in binary form ▯ Are more complex ▯ Need a query language to access and manage data, object query language (OQL) is similar to structured query language 3) Multidimensional Databases What is a multidimensional database? ▯ Stores data in more than two dimensions ▯ Organize data in cube format ▯ Each data cube has a measure attribute which is the main type of data that the cube is tracking ▯ Feature attributes describe the measure attribute in some meaningful way What are the advantages of multidimensional databases? ▯ Can be easily customized to provide information to a variety of users ▯ Can process data much faster than pure relational databases can 4 ▯ Example, Oracle Corporation Database Management Systems: Basic Operations ▯ Database management system (DBMS) interacts with the user, other applications, and the database to capture and analyze data ▯ FOUR main OPERATIONS: 1. Creating databases and entering data 2. Viewing and sorting data 3. Querying (extracting) data 4. Outputting data Creating Databases and Entering Data How do I create a database with DBMS? ▯ Define the data to be captured ▯ Create description of the data (data dictionary or data schema) ▯ Data dictionary defines the name, data type, and length of each field in the database How do I know what fields are needed in my database? ▯ Each field should describe a unique piece of data and should never combine two separate pieces of data What does a data dictionary look like, and how do I create one? ▯ In Microsoft Access data dictionary is called Field Properties Box ▯ To create one there are 4 steps: 1. Create a field name (field names should be unique within a table 2. Define a data type for each field 3. Set a max field size for the field 4. Set a default value which is the value the database uses for the field unless the user enters another value ▯ Repeat these steps for each field in the table ▯ Metadata is data that describes other data What happens if I forget to define a field in the data dictionary or if I want to add another one later? ▯ You can add additional fields as needed but this does not negate the need for proper planning and design of a database Inputting Data How do I get data into a database? ▯ After creating a data dictionary for each table in the database and establish the fields you want the database to contain ▯ Create individual records, and input data by keying it into the database ▯ A better way is to import data electronically from other application files ▯ Databases use filtering to determine if the data is the correct format How can I make manual entry into a database more convenient? ▯ Create an input form which provides a view of the data fields to be filled, with appropriate labels to assist database users in populating the database 5 Data Validation How can I ensure that only valid data is entered into the database? ▯ Validation is the process of ensuring that data entered into the database is correct and complete ▯ Validation Rule is a rule that is set up in a database to alert the user to the possible wrong entries How does a range check work? ▯ Range check ensures that the data entered into the database falls within a certain range of numbers ▯ Field constraint is any property that must be satisfied for an entry to be accepted into the database field What does a completeness check accomplish? ▯ Ensures  that  all  fields  defined  as  “required”  have  data  entered  into  them What is the function of a consistency check? ▯ Compares the values of data in two or more fields to see if these values are reasonable How are alphabetic and numeric checks used? ▯ Alphabetic check confirms that only textual characters are entered in a field ▯ Numeric check confirms that only numbers are entered in the field Viewing and Sorting Data How can I view the data in a database? ▯ Displaying the data on-screen and browsing through the data How can I reorder records in a database? ▯ Sort a database into order you need What if I want to find a particular piece of data in a database? ▯ Browsing records: for small databases ▯ Request the data you are seeking: for large databases Extracting or Querying Data What is a query? ▯ A query is a question or inquiry ▯ A database query is a question you ask the database so that it provides you with the records you wish to view Is querying a database as simple as just asking the proper question? ▯ A software uses a query language which retrieves and displays records ▯ Structured Query Language (SQL) Do I have to learn a query language to develop queries for my database? ▯ There are Wizards Outputting Data How do I get data out of a database? ▯ Viewable electronic report (summary report) Can I transfer data from a database to another software application? 6 ▯ Exporting data involves putting it into an electronic file in a format that another application can understand Relational Database Operations ▯ The link between tables that defines h
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