IS5413 Chap.1 Data, Metadata and the Database Environment
Data, Metadata and the Database Environment
Three words that look like synonyms and are not
The course opens on a distinction that looks pedantic until the first time it costs you a mark. Data are the stored form taken by objects and events that matter to somebody, whether structured values or unstructured content.
Information is what those representations become once they are processed and placed in context, so that they increase the knowledge of the person reading them. Metadata is the description that supplies the context: the type of a field, its length, its allowable values and the unit that owns it. A class roster is the standard illustration.
Names, identifiers, majors and grade averages sitting on a page are data; the same page read as a workload for one section of one course in one semester is information; and the row that says a grade average is a decimal of three digits bounded at zero and four is metadata.
Why the third one is the one that gets forgotten
Metadata is what allows two applications written by two different teams to agree on what a field means.
Without it, agreement is an accident that survives until somebody changes a program. This is also why the centralised storehouse for metadata, the repository, appears on the published list of environment components alongside the management software itself.
A question asking you to identify the components of a database environment is not answered by naming software: the published list mixes tools, the repository, the management system and the stored data with the people who maintain it, develop against it and use it.
The human roles are part of the specification because it is those people who decide what the metadata says.
Four separable faults in file processing
Before the database approach each department wrote its own programs against its own files, with an order filling system, an invoicing system and a payroll system each maintaining a private copy of the customer or inventory data. Four named weaknesses follow.
Program data dependence means every program carries its own description of the files it reads, so a change to a field length is a change to every program touching it. Duplication means the same customer exists in several files and the copies drift. Limited sharing is organisational rather than technical: a department that owns a file controls access to it.
High maintenance cost follows from the other three, with the published figure putting up to eighty per cent of an information systems budget into program maintenance.
What replaces it, and what that costs
Three things substitute for the file arrangement and only the third is software: shared data move to one central store, a controlling agent takes responsibility for access, update and integrity, and storage becomes standardised.
The management system is the enabler of that arrangement, managing the data resource the way an operating system manages hardware. The published advantages are mostly organisational, led by program data independence and planned rather than accidental redundancy.
The published costs are equally concrete: specialised staff, installation and management overhead, expensive conversion from legacy files, explicit backup and recovery planning, and the friction that follows when a privately owned resource becomes centrally controlled.
What this chapter covers
- 01
Data against information against metadata
- 02
The repository and why it sits beside the management system
- 03
Program data dependence as distinct from duplication
- 04
Limited sharing as an organisational fault
- 05
Enterprise and project level data models
- 06
The published costs and risks of the database approach
Worked example · free
Separate the four faults in one scenario
- 2Assign the format difference and the update failure to their faults.
- 2Assign the access barrier to its fault.
- 2Say which fault survives deduplication, and why.
Key terms
- Data
- The stored form of objects and events the organisation cares about, held either as structured values such as numbers and dates or as unstructured content such as images and documents.
- Information
- What data becomes once processing and context have made it useful to the person reading it. Context is supplied by metadata.
- Metadata
- Data about data: the type, length, allowable values, description and owning source of each item. It is what makes a shared definition possible.
- Repository
- The centralised storehouse in which metadata is held for the whole environment, listed as a component of the database environment in its own right.
- Program Data Dependence
- The coupling that exists when each program carries its own description of the files it reads, so that a change to a data structure forces a change to every program.
- Enterprise Data Model
- A high level, organisation wide view of major entity types and their relationships, drawn without attribute detail as the first step in database development.
Data, Metadata and the Database Environment FAQ
What is the difference between data and information?
Data are the stored representations themselves; information is what they become once processed and placed in context so that somebody's knowledge increases. The examinable consequence is that the same stored values are data or information depending on what surrounds them, which is why metadata is treated as a separate idea rather than as a kind of data.
A short question here usually supplies a table and asks you to say which is which, and the answer turns on whether the context needed to interpret the values is present.
Why is duplication treated as a separate fault from data dependence?
Because the two survive different repairs. A system holding exactly one copy of every fact still suffers dependence, since the description of that copy remains inside each program. A system whose programs read their descriptions from a repository still suffers duplication if the data itself is copied.
The database approach happens to remove both, which is why students merge them, and why a question naming only one of them is testing whether you can keep them apart.
Exam move
Write the four file processing faults as four separate sentences, each with a symptom you could observe from outside the system. Then take any information system you use and try to assign one real annoyance to each fault. The exercise is quick and it makes the distinctions stick better than rereading the list, because the faults differ by what evidence would reveal them.
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