I am a bit confused with the partial keys. 'Database System Concepts by Korth' says the following:
Although the weak entity set does not have a primary key, we nevertheless need a means of distinguishing among all those entities in the weak entity set that depend on one particular strong entity. The discriminator of a weak entity set is a set of attributes that allows this distinction to be made. The discriminator of a weak entity set is also called the partial key of the entity set.
My confusion is that if the discriminator/partial keys of weak entities are able to uniquely identify the set of attributes, then it should be called primary key, instead of partial keys, as primary keys are those which can uniquely identify all the attributes of a relation.
Also, while surfing the web, I came across a definition of partial key, which says:
'A partial key is a key using which all the records of the table can not be identified uniquely'
It raises a question in my mind, that suppose if a table consists of a primary key which is made up of two or more attributes, then if we pick up a single attribute from this, then will it be called partial key, as that attribute is part of a primary key, but by itself it can't uniquely identify all attributes in a relation.
The definition doesn't say that "the discriminator/partial keys of weak entities are able to uniquely identify" within a table. It says that one identifies a weak entity within a particular strong entity.
Technical terms only mean what they are defined to mean in a certain context of assumptions, including other definitions. You can't expect the same term to mean the same thing everywhere. You can't just look at the text of a definition & make assumptions about what situations it applies to & what its technical terms mean or even whether a word is used in a technical or everyday meaning. When someone uses a term you have to make sure that you know what they mean by it.
A relational superkey uniquely identifies a row. A CK (candidate key) is a superkey that contains no smaller superkey. A PK (primary key) is just some CK you decided to call the PK.) So being unique is not a reason to call something a PK or CK. (An SQL PK/UNIQUE is analogous to a relational superkey.)
The book method generates discriminators that are not superkeys. So we can say that it agrees with the web definition--for cases that come up in that method. But if a method allowed generation of discriminators that were CKs or PKs then its use of that textbook wording would define "partial key" to be a different sort of thing than the web definition. Such a method couldn't use (relational) "PK" for a strong id plus discriminator, because it would be a superkey but not a CK or PK. (But it could still use SQL "PK" since that approximately means primary superkey.)