Information Technology • Databases and Files

File Access Visualiser

Collisions

File Access Visualiser — Explanation

How to use it. In Access methods, type a key (or pick a preset) and press Search, Add or Delete. All four files do it at once: each record, index entry or slot read lights up, writes show in amber, and the counters show the reads and writes each needed. Choose how hash collisions are handled with the toggle. Batch update steps through updating a master file from a transaction file.

The four organisations

Master and transaction files

A master file holds the main, fairly permanent data, in key order. A transaction file collects the changes (updates, additions, deletions) over a period. In batch processing the transaction file is sorted into the same key order, then both are read in step to write a new master file; transactions that don't match go on an error report. The old master and the transaction file are kept: the grandfather–father–son system means a lost master can be recreated.

Common exam mistakes: mixing up serial and sequential; saying a sequential search always reads every record (it stops once it passes the key); saying hashing never needs more than one read (collisions); and forgetting that the transaction file must be sorted before a batch update.

Objective: Cambridge International AS & A Level Information Technology (9626), database and file concepts: serial, sequential, indexed sequential and random (direct) file organisation and access, hashing and collisions, master and transaction files, and batch updating.

Where this fits

  • Cambridge: Cambridge A Level Computer Science (9618); Cambridge A Level Information Technology (9626); Cambridge AS Level Information Technology (9626) Goes beyond Cambridge A Level Computer Science (9618): Indexed sequential files and batch master-file updates go beyond 9618 13.2.

File Access Visualiser — Key Terms

Key concepts in English, with te reo Māori, Chinese (Simplified) and Korean.

EnglishTe reo Māori中文（简体）한국어What it means on this page
Keykī键키The field that identifies each record, such as a member’s ID: the files are sorted, indexed or hashed on it.
Row (record)haupae / pūkete行행One entry in a file: here, one library member.
Serial Fileno attested term串行文件 (chuànxíng wénjiàn)직렬 파일 (jillyeol pail)A file whose records are stored one after another in the order they were added.
Sequential Fileno attested term顺序文件 (shùnxù wénjiàn)순차 파일 (sun-cha pail)A file whose records are stored in order of a key field.
Indexed Sequential Fileno attested term索引顺序文件 (suǒyǐn shùnxù wénjiàn)색인 순차 파일 (saegin sun-cha pail)A file in key order, in blocks, with an index of the blocks, so it can be read in order or a record can be found through the index.
Random Access Fileno attested term随机存取文件 (suíjī cúnqǔ wénjiàn)임의 접근 파일 (imui jeopgeun pail)A file where a record's address is worked out from its key (by hashing), so it can be read directly, without reading others first.
Hashing Algorithmno attested term哈希算法 (hāxī suànfǎ)해시 알고리즘 (haesi algorijeum)A calculation that turns a record's key into the address where it is stored, such as key MOD 17.
Collisionno attested term冲突 (chōngtū)충돌 (chungdol)When two different keys are hashed to the same address, so one record must be stored somewhere else.
Overflow Areano attested term溢出区 (yìchūqū)오버플로 영역 (obeopeullo yeongyeok)A separate part of a file for records that cannot be stored in their proper place, such as after a hash collision.
Indexno attested term索引 (suǒyǐn)색인 (saegin)A table of keys and where to find them, used to go to the right part of a file without reading it all.
Master Fileno attested term主文件 (zhǔ wénjiàn)마스터 파일 (maseuteo pail)The main, fairly permanent file of records, usually in key order, kept up to date from transaction files.
Transaction Fileno attested term事务文件 (shìwù wénjiàn)트랜잭션 파일 (teuraenjaeksyeon pail)A file of the changes (updates, additions, deletions) collected over a period, used to update a master file.
Batch Processingno attested term批处理 (pī chǔlǐ)일괄 처리 (ilgwal cheori)Collecting data over a period and processing it all together in one run, without the user taking part.
Grandfather–Father–Sonno attested term祖父-父-子备份 (zǔfù-fù-zǐ bèifèn)조부-부-자 백업 (jobu-bu-ja baegeop)A backup system that keeps the last three generations of a master file, with their transaction files, so a lost file can be recreated.

On the te reo Māori column. Terms marked as gaps have no attested equivalent in the sources checked — Karaitiana Taiuru's Dictionary of Māori Computer and Social Media Terms, Paekupu, the Reserve Bank's te reo financial glossary, NZQA and Te Aka. No coinage is printed as though it were established; where a class needs one, commission it from Te Taura Whiri i te Reo Māori and credit the translator. Te reo Māori is not italicised and takes no plural "s".