STORAGE & RETRIEVAL

STORAGE & RETRIEVAL

• Storage & retrieval occur in all information systems.
• It is critical though in maintaining large data stores.
• Storing saves data/ retrieving reloads data.
• DBMSs separate data and it's management.
• This includes storage & retrieval, from software that processes it.

DATA INDEPENDENCE

• This separation so known as "Data independence"
• DI provides the ability of data & it's organisation to be altered
• Without affecting or changing the software app that processes the data

WHEN S&R PROCESSES ARE VIEWED

• at their most basic level, it is true to sat that the actual data is
• not changed, rather the way it is represented changes
• Eg data on a hard disk is stored using magnetic fields
• when this data is reloaded, the retrieval process converts
• these magnetic fields into electrical signals for transmission

CONSIDER THIS

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GROUP TASK

• Construct a set of DFDs, similar to fig 2.41&2.42
• that describe the data flows & processes performed by
• a web server.

NEXT UP

• Types of storage hardware
• Security techniques
• Searching and sorting

STORAGE HARDWARE

ON-LINE & OFF-LINE STORAGE

• Off-line storage cannot be accessed until it is mounted into a drive
• Eg magnetic tape, CDS/DVDS and other portables like USB memory.
• On-line can be available immediately to any connected computer.
• Eg hard disks within a computer and network/internet storage.

STORAGE TYPES

• Magnetic
• RAID (Redundant Array of Independent Disks)
• Cartridge & Tape
• Tape Library
• Optical Storage

SECURING DATA

• Backup & Recovery✔️✖️
• Physical security✔️✔️
• Usernames and passwords✔️✔️
• Encryption & Decryption✖️✔️
• Restricting access✖️✔️

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• Records locked in DBMS views✔️✖️
• RAID (mirroring only)✔️✖️