Knowing about the SAS data object hierarchy and locking
concepts will help you to understand the behavior of explicit locks that you
set by using the LOCK statement or a LOCK command and the conditions under
which implicit locks are set automatically. Also explained are the effects
of locking on other operations.
When you perform a SAS operation,
the SAS/SHARE server controls what data object is locked and how the data
object is locked. This allows you to access the data objects and denies access
to those data objects by other users for the duration of the operation.
Hierarchy of SAS data object Types
shows the SAS data object type hierarchy.
Hierarchy of SAS data object Types
![[IMAGE]](./images/01319367.gif)
![[1]]( ../common/images/sym01.gif)
SAS data library- a collection of one or more SAS files that
are recognized by SAS. Each file is a member of the library.
![[2]]( ../common/images/sym02.gif)
Member- a file in a SAS data library that may be
one of the following types:
- SAS data file
- SAS data view
- SAS utility
file
- SAS data catalog.
- SAS data file
- a SAS data set that contains both the data
values and the descriptor information. SAS data files are of member type DATA.
- SAS data view
- a SAS data file in which the descriptor
information and observations are obtained from other files. SAS data views
store only the information that is required to retrieve data values or descriptor
information. SAS data views are of member type VIEW.
- SAS utility file
- a SAS file that stores information that
is private to a component of SAS. Examples include SAS/ACCESS descriptors,
MDDB (Multi-Dimensional Data Base) files, and DMDB (Data Mining Data Base)
files.
- SAS catalog
- a SAS file that stores many different kinds
of information in smaller units called entries. Some catalog entries contain
system information such as key definitions. Other catalog entries contain
application information such as window definitions, help windows, formats,
informats, macros, or graphics output.
![[3]]( ../common/images/sym03.gif)
Observation- often referred to as a record, the horizontal
component of a SAS data file. An observation is a collection of data values
associated with a single entity, such as a customer or a state. Each observation
contains one data value for each variable in the data file.
- Entry
- a unit of information that is stored in
a SAS catalog.
|
| How SAS Data Objects Are Accessed and Used |
The type of lock that a server sets
on a member or an observation is affected by how the operation accesses and
uses the SAS data object type. The ways to access a data object are:
| input |
to read data |
| update |
to change the values of variables |
| output |
to add new variables with values |
| utility |
to change the header information
of the file. |
Each SAS operation has a default behavior for each object
that is accessed and the way that the object is accessed. For example, given
that the server engine permits observation locking and the observation is
not already locked, the server can open and lock an observation in a data
set. If the engine does not support observation locking, the engine locks
the member (above the observation) instead.
The lowest hierarchical level at which data can be locked
varies according to the engine that is used to access the data:
- The Version 7 engine (V7) and the Version 8 (default)
engine (V8) allow locking at the library, member, and observation level.
- The V7TAPE, the V8TAPE, and other sequential engines
do not support locking below the member level.
- Any engine that does not support access to SAS
catalogs does not support locking at any level.
- View engine default-locking behavior is based
on how the view is created; for example, by using the DATA step, by using
the SQL procedure, or by using the ACCESS procedure, which is available through
SAS/ACCESS. Likewise, the specific SAS/ACCESS engine that is used depends
on the DBMS. See your SAS/ACCESS documentation for information about view
engine default-locking behavior.
Effects of Object Locking on Other Client Operations
shows the combinations of objects that are locked, how objects are locked,
and the effects on other client operations.
Effects of Object Locking on Other Client Operations
|
What Object Is
Locked |
How the Object Is Locked |
|
Input |
Update |
Output |
| Member |
Other operations can read the data set but cannot open
it for update or output. |
No other operations can access the data set. |
No other operations can access the data set. |
| Observation |
Other operations can read or update the data set but
cannot open it for output. |
Other operations can read or update the data set but
cannot open it for output. |
No other operations can access the data set. |
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
