A data dictionary is a special file or set of tables that contains which of the following information about the fields in all files or tables of a database?

Introduction / Context:
A data dictionary, sometimes called a system catalog or metadata repository, is a core component of database systems. It stores descriptive information about the structure of the database, rather than the actual user data. This metadata helps the database engine and tools understand how to interpret, validate, and present the stored data. This question asks what kind of information a data dictionary contains about fields in all files or tables.

Given Data / Assumptions:

We are dealing with a database or file system that maintains a data dictionary or catalog.
The dictionary describes fields (columns) used in various files or tables.
Field descriptions typically include the name, the data type, and the size or width in characters or bytes.
Additional metadata such as constraints or default values may also exist, but the question focuses on name, type, and width.
The options present different subsets of these pieces of information.

Concept / Approach:
In practice, a data dictionary holds comprehensive metadata about database objects. For fields, this includes the column name, data type, length or precision, and often other properties. It is not limited to a single attribute such as width or data type. The correct answer therefore must mention all of the main field attributes, not just one. Choosing the option that combines name, type, and width best matches this common understanding of a data dictionary.

Step-by-Step Solution:
Step 1: Recall that database tools and applications need to know how to interpret each field. They need the field name for identification, the data type to know how to handle values, and the width to know storage or display limits. Step 2: Recognize that the data dictionary is the central repository for this metadata, so it must store all of these attributes. Step 3: Review the answer options and identify the one that states that the data dictionary contains the name, data type, and width of all fields. Step 4: Confirm that options that mention only one of these attributes are incomplete and therefore incorrect.

Verification / Alternative check:
If you have access to a relational database, you can query system tables such as INFORMATION_SCHEMA.COLUMNS. The results will include column names, data types, maximum lengths, and other metadata. This is a concrete example of a data dictionary in action and confirms that a full description of each field involves name, type, and width information.

Why Other Options Are Wrong:
Storing only the width of fields without names or data types would be useless because you would not know which field each width belongs to or how to interpret the data.
Storing only data types or only names is similarly insufficient because applications require both identifiers and type information along with size constraints to function correctly.
Therefore, any option that mentions only one attribute cannot describe a real data dictionary.

Common Pitfalls:
A common misunderstanding is to think of the data dictionary as only a list of table and column names, when in fact it contains much richer metadata. Another pitfall is to ignore the data dictionary when designing queries or tools, instead hard coding assumptions about types and lengths, which can cause problems when the schema changes. Relying on the data dictionary helps maintain flexibility and accuracy.

Final Answer:
A data dictionary contains the names, data types, and widths of all fields in all files, along with other metadata.