This article needs additional citations for
verification. (August 2021) |
In computer science, a field (data field) is a data element of a record.
In a relational database, data is arranged as sets of records, a.k.a. rows, where each consists of the same sequence of fields.
In object-oriented programming, an object is a record that consists of data and function fields. [1]
The following Java class has 3 fields: firstName, lastName, and age.
public class Person
{
private String firstName;
private String lastName;
private int age;
}
In row-based storage, fields are typically either fixed or variable length.
Fields that contain a fixed number of bits are known as fixed length fields. A four byte field for example may contain a 31 bit binary integer plus a sign bit (32 bits in all). A 30 byte name field may contain a person's name typically padded with blanks at the end. The disadvantage of using fixed length fields is that some part of the field may be wasted but space is still required for the maximum length case. Also, where fields are omitted, padding for the missing fields is still required to maintain fixed start positions within a record for instance.
A variable length field is not always the same physical size. Such fields are nearly always used for text fields that can be large, or fields that vary greatly in length. For example, a bibliographical database like PubMed has many small fields such as publication date and author name, but also has abstracts, which vary greatly in length. Reserving a fixed-length field of some length would be inefficient because it would enforce a maximum length on abstracts, and because space would be wasted in most records (particularly if many articles lacked abstracts entirely).
Database implementations commonly store varying-length fields in special ways, in order to make all the records of a given type have a uniform small size. Doing so can help performance. On the other hand, data in serialized forms such as stored in typical file systems, transmitted across networks, and so on usually uses quite different performance strategies. The choice depends on factors such as the total size of records, performance characteristics of the storage medium, and the expected patterns of access.
Database implementations typically store variable length fields in ways such as
If a varying-length field is often empty, additional optimizations come into play.
This article needs additional citations for
verification. (August 2021) |
In computer science, a field (data field) is a data element of a record.
In a relational database, data is arranged as sets of records, a.k.a. rows, where each consists of the same sequence of fields.
In object-oriented programming, an object is a record that consists of data and function fields. [1]
The following Java class has 3 fields: firstName, lastName, and age.
public class Person
{
private String firstName;
private String lastName;
private int age;
}
In row-based storage, fields are typically either fixed or variable length.
Fields that contain a fixed number of bits are known as fixed length fields. A four byte field for example may contain a 31 bit binary integer plus a sign bit (32 bits in all). A 30 byte name field may contain a person's name typically padded with blanks at the end. The disadvantage of using fixed length fields is that some part of the field may be wasted but space is still required for the maximum length case. Also, where fields are omitted, padding for the missing fields is still required to maintain fixed start positions within a record for instance.
A variable length field is not always the same physical size. Such fields are nearly always used for text fields that can be large, or fields that vary greatly in length. For example, a bibliographical database like PubMed has many small fields such as publication date and author name, but also has abstracts, which vary greatly in length. Reserving a fixed-length field of some length would be inefficient because it would enforce a maximum length on abstracts, and because space would be wasted in most records (particularly if many articles lacked abstracts entirely).
Database implementations commonly store varying-length fields in special ways, in order to make all the records of a given type have a uniform small size. Doing so can help performance. On the other hand, data in serialized forms such as stored in typical file systems, transmitted across networks, and so on usually uses quite different performance strategies. The choice depends on factors such as the total size of records, performance characteristics of the storage medium, and the expected patterns of access.
Database implementations typically store variable length fields in ways such as
If a varying-length field is often empty, additional optimizations come into play.