Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

12 ipt 0203 Storage and Retrieval

Notes on 2.3 of the HSC IPT course

Related Books

Free with a 30 day trial from Scribd

See all
  • Be the first to comment

12 ipt 0203 Storage and Retrieval

  1. 1. Information Systems & Databases 2.3) Storage and Retrieval
  2. 2. • A database management system (DBMS) is the software used to access, create and modify a database. • There are two main ways of accessing data: • sequential • processes in sequence • slower than direct • cheaper • e.g. magnetic tape
  3. 3. • direct • can go straight to data • faster than sequential • more expensive • A distributed database is a database located at more than one site. • It reduces data transmission costs. • They need to be synchronised often. • There are many types of storage media. They can include:
  4. 4. • hard disc – a disc made of metal or glass and covered in a magnetic material (hard drives) • optical disc – a plastic disc with a reflective metal layer (CD, DVD, Blu-ray) • magnetic tape – a long strip of plastic coated with a thin layer of magnetic material; they are inexpensive and sequential in nature.
  5. 5. • Encryption is the process of encoding data. • Decryption is the process of changing it back. • Encrypted data is an effective way to ensure data security. • There are two main kinds of encryption: • asymmetric –require different keys for encrypting and decrypting
  6. 6. • • • • • symmetric –uses the same keys for encrypting and decrypting A DBMS contains backup and recovery capabilities to guard against data loss. A backup is another copy of the data that can be used to rebuild the system. Ideally, the backup should be in a secure and different location. Data security measures can also include:
  7. 7. • user accounts and passwords • personal ID objects like magnetic cards • biometric devices (e.g. fingerprint scan, voice recognition) • firewall – mix of hardware & software • offline data access – no Internet presence
  8. 8. • Sorting is the process or arranging the data in meaningful way. • Sorts can be either ascending or descending. • Ascending is: • alphabetical • smallest to largest • earliest to latest • Descending is the reverse.
  9. 9. • Searching the database is performed through constructing a query. • A query is a search for records that meet certain conditions (or criteria) • A simple query is constructed in the form of : <Field Name><Operator><Criteria> • A common method is called query by example (QBE) • This is where you put characters into a search field (with wildcards if needed)
  10. 10. • Wildcard characters represent one or more unknown characters. • An asterisk (*) substitutes for any number of characters while a question mark (?) substitutes for only one character. • Operators represent the action that is performed in the query. • They can be either relational or logical. • Relational operators are symbols indicating the relationship between two expressions.
  11. 11. • They include: >, <, =, <>, <=, >= • Logical operators are used to combine queries. • They include AND, OR & NOT. • AND requires each condition to be met while OR will be satisfied with any condition. • E.g. Year = 10 AND Gender = “M” will return only Year 10 males while Year = 10 OR Gender = “M” will give all the males in the school and all of Year 10
  12. 12. • A query language is a specialised language designed to search a database. • Structured query language (SQL) is a query language that uses the following keywords: • SELECT • FROM • WHERE • ORDER BY [COPY Table 2.4, p.59]
  13. 13. • When using SQL it is important to use the correct syntax. • This includes: • keywords written in upper case • fields separated by commas • entity and attribute separated by a full stop • criteria or data items inside quotation marks unless a number
  14. 14. • E.g. SELECT students.fname, students.lname, classes.classname FROM students, classes WHERE Year>10 AND Gender = “F” ORDER BY lname [asc], fname [asc] [Complete LA 2 (c) and (d), p.63] • A search engine is a database of indexed websites.
  15. 15. • Indexing creates a table of information about the location of data. • This table is built by regularly scanning the Internet for new sites and looking at keywords and metadata. • This scanning is often carried out by programs called spiders, crawlers or bots.