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I was reading the Chapter 1 of the 7th edition of Database System Concepts and ran into this:

• Schema and physical-organization modification. The DBA carries out changes to the schema and physical organization to reflect the changing needs of the organization, or to alter the physical organization to improve performance.

Is it true that database administrators can access the physical schema and change it or have I misunderstood what is cited above?

heretoinfinity
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    if the d´rdms supports it see https://en.wikipedia.org/wiki/Physical_schema the DBA can usually change anything thas a specific rdms and os allows – nbk Sep 12 '20 at 21:08

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One of the innovation of the relational model was to separate thr logical view that programmers see (tables of columns) from the physical storage (files on disks). To function the DBMS must be aware of both and hence must have the ability to amend both. So yes, if you define DBA as "someone who manages a DBMS" a DBA can change the physical schema.

Most DBMS implement a permission system. Different permissions will affect the creation of tables and the use of disks. In smaller teams it may be that one person has granted both of these permissions. In larger teams it becomes more likely the tasks are separated. You will find application DBAs defining tables and queries and operational DBAs looking after disks and CPUs. In businesses dealing with financial data or PII it may be that neither of those roles has access to any of the data.

Michael Green
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There is two sorts of DBA:

  • dba for the production
  • dba for the design

for production, the dba should never alter the design the database schema. This is the case when applications cames from software editors

for design, the dba is responsible for the best design of the database internally made for a specific demand

Sometime the dba has the two hats...

SQLpro
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