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Flashcards by Malachy Moran-Tun, updated more than 1 year ago
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| Question | Answer |
| What is Capturing Data, and what Methods can be Used? | > Data has to be inputted (either automatically or manually) before it is added to a database > Manual methods include transcribing data from a form > Automatic methods include: MICR (Magnetic Ink Character Recognition, used for cheques), OMR (Optical Mark Recognition), OCR (fuck 'em... i mean Optical Character Recognition), or NFC (Near Field Communication) > Data may be selected / filtered, only capturing those that match certain criteria before being added to the database |
| How can Data be Transferred between Systems without the need for Human Intervention? | > EDI - Electronic Data Interchange > Documents that use standard formatting can be exchanged electronically > Transaction software processes the information |
| What is a Transaction? | A single, logical operation on data |
| What is ACID? | > A set of properties that guarentee transactions are reliably processed > Atomicity - transaction is processed in its entirety or not at all (e.g., in powercuts or crashes, the transaction does not proceed, or only process part of it) > Consistency - no transaction has violate the defined rules for maintaining referential integrity > Isolation - a transation cannot be interrupted by another, and concurrent transations lead to the same results as transactions happening one after another > Durability - similar to atomicity, once a transaction has been committed, it is irreversable, even if there is a system fail |
| What is Record Locking? | > Prevents simultaneous access to objects in a database, so multiple people cannot update it inconsistently > E.g., a record is locked when a user is editing it or retrieving data from it |
| What is Serialisation? | > Ensures transactions do not overlap in time - i.e., they cannot interfere with eachother, or lead to updates being lost |
| What is Timestamp Ordering? | > Serialisation technique > Objects in a database are given a read and write timestamp, updated when needed > When a transaction starts, it reads data from a record, setting the read timestamp. Before data is written, it checks to see if the timestamp has updated since, if so, it does not continue as a transaction is currently taking place |
| What is Commitment Ordering? | > Serialisation technique > Ensures that transactions are not lost when more than one person is accessing the same database object > Transactions are ordered in terms of their dependencies on eachother, as well as by time |
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