1. What does DDS stand for?
Data Description
Specifications.
2. What are the types of files?
·
Data base files
·
Device file
·
DDM files (Distributed Data Management files)
·
Save files
Database files
This
is the actual database for AS/400.
It
includes PF, LF, and Field Reference Files
Device files
A device file contains the
description of how to use the physical devices such as display stations,
printer and tape devices. E.g. Display file, printer file.
DDM files
The DDM files are employed when
we tries to access a file from a remote system to our current system. The
current system is called source system and the remote system is called target
system. Just like other database files the DDM files are to be opened before
they are used in program. After they are created an access path is created,
thro’ which the target system is accessed.
DDM files serve as a medium,
connecting the program running on source system and the file on the target
system.
They are used to
·
Copy a file from one system to another.
·
Manage file on a remote system.
·
Access data from a remote system.
Save files
They are used to hold the data in
a format for back up and recovery purposes.
3. What is Source
Physical File?
Source physical file is also a
file, which has one or more files included in it. It is just like a directory
and it contains many members. The members are like a various programs residing
in the directory. CRTSRCPF is used to create source physical file.
4. What is a
member?
A member is a subset of data
within a file.
All
program, files within a source file are called member for that file.
5. What is a
Physical File?
It is an object its type is PF,
that physically occupies memory space for the purpose of store and retrieve
data. It is a single record format. CRTPF command is used to create a physical
file. Maximum number of fields included in a PF is 8000. Maximum no of key
fields included is 120.
6. What are the
four level entries of PF?
There is File level entries,
Record level entries, Field level entry, and Key level entry.
File
level entry keywords are UNIQUE, LIFO, FIFO, FCFO [First Change First
Out], REF.
In
record level entry, we can give the Record format name.
In the
field level entry, we can define the field names, types and size.
In the
Key level entry, we can define the key field.
7. UNIQUE –
explain.
It is a
file level keyword specified not to allow a duplicate key in a keyed file.
8. Can a physical file contain more than one member, and how is it
accessed?
Yes, by using OVRDBF (___) MBR (___)
9. When a PF is compiled and
default values used how many members does it have?
One
10. What does the DSPPFM command
do?
Displays a list
of records on the CRT from the physical file.
11. Explain the use of DSPFFD.
To display a
physical files record layout structure.
12. How would you change the attribute of file?
CHGPF command is
used. By this we can change the length of field, wait time, field name, etc.
13. DSPDBR – Expalin.
Display Database
Relation. It tells the no. of logical file that are built over a specified PF.
14. What is the CPYF command
used for?
a.) To print all
records in a physical file,
b.) To transfer
records from one PF object to another PF object.
15. What is the purpose of the
*MAP and *NOCHK in the CPYF command?
a.) To transfer
data byte by byte.
b.) To transfer
data field by field regardless of field names.
16. How to copy a
ten specified records from one file to another file?
By using CPYF command we can copy
record from one file to another file. If we want to copy from one position to
another position, we have to give the starting
position and ending position. If
we want to copy based on condition, we have to give the criteria on the sql statement.
17. ADDPFCST –
explain
ADDPFCST is a command that is
used to define the Constraint on your physical file. The constraint has several
types. These are REFCST, UNQCST and PRIKEY. By the by, this command is helps to
define Update rules and Delete rules.
18. How you will
establish Referential Integrity in AS/400?
Referential integrity is a
relation between two files, the parent file and the dependent file. The
relationship establishes that every record in the dependent file has to have a
matching record in the parent file.
By using
ADDPFCST command, we can establish in AS/400.
Let we have two PF namely Master
and Invoice the fields in Master are CustNo, CustName…. And Invoice PF has the
fields are Custnum, Invno, Invdate…
Now we
are going to establish referential constraint to those files.
File : Invoice
Library : xxxxxx
Constraint type :*REFCST
Constraint Key :Custnum
Constraint Name :*GEN
Parent file :Master
Library :xxxxxx
Parent Key :Custno
Delete Rule :*cascade
Update Rule :*restrict
Thus the
referential constraint has been created
19. Explain DSPFD
and DSPFFD.
Display file description is used
to list the total number of records in the files remaining records to be added
and other related information about the file.
Display
file field description is used to listing details about individual fields
20. What is
Normalization?
Removing replication of data by
applying integrity rules is known as Normalization. Suppose a table have empno,
empname, age, address, dob, monthyear, salary fields and the table has the
following data
101 raja 28 dsfsdfsdfsd 10-4-77 0102 54354
101 raja 28 dsfsdfsdfsd 10-4-77 0202 54354
101 raja 28 dsfsdfsdfsd 10-4-77 0302 54354
101 raja 28 dsfsdfsdfsd 10-4-77 0402 54354
101 raja 28 dsfsdfsdfsd 10-4-77 0502 54354
101 raja 28 dsfsdfsdfsd 10-4-77 0602 54354
101 raja 28 dsfsdfsdfsd 10-4-77 0702 54354
Here the name,
age, address, DOB are fixed data. By feeding these data again and again the
table size will be expand. So we can put these data another table by using
integrity rules. So the table can be split by
PF01 => Empno, empname, age,
address, DOB where empno is KEY
PF02 => Empno, Month year,
salary
Now PF01 can has only one record
and PF02 has 7 records.
21. How you list
all LF of PF?
DSPDBR is used to display all the files, which are related to the
physical file. It display all the logical files that are referring the physical
file and also list the child table, if it has a relationship with that file.
22. What is a
Logical File? And give its types?
It is used to access the data in
a physical file.
It cannot exist with out a
physical file. It can have multiple record formats. By using LF we can change
the key field and attribute size. We can filter the data with criteria by using
select and omit command. CRTLF command is used to create a LF. It accesses the
data by the access path.
There are
two types of LF
Join
Logical files.
Non Join
Logical files.
23. What are the
two types of logical files and its difference?
There is
Join Logical files and Non-Join Logical files.
|
Join Logical
Files
|
Non Join Logical
File
|
|
Impossible to insert, update and deleting records.
|
Able to insert, update and deleting records.
|
|
Up to 32 record format can be specified
|
Only one record format can be specified
|
|
Commitment control is possible
|
Commitment control can’t be used
|
24. What are the 6
level entries of LF?
They are
File level
Record level
Join level
Field level
Key level
Select/omit level entries.
25. Does a logical file contain
data?
No, it contains access
path information only.
26. Explain
Non-Join Logical file.
Logical files, which can be
derived data from one or more than physical file. But not joining themselves is
known as Non-join logical file. If it retrieves data from one physical file,
then it is single record format and if it is retrieve data from multiple
physical file it has multiple record formats.
There are five level entries in
Non-Join Logical file.
File level entries
Record level entries
Field level entries
Key level entries
Select / Omit field level
entries.
27. DYNSLT –
explain.
Dynamic select. It is a file
level keyword used to select records during execution time and the record will
not be selected until the file is opened in program.
28. Explain Join
Logical file.
A Join Logical file that combine,
in one record format from two or more physical files. A PF can’t be changed
through a JLF. We can’t insert, update and delete records. DFU can’t be used to
display a JLF. Only one record format can be specify. Commitment control can’t
be used.
Let PF01 has EmpNo, Empname
fields and PF02 has EmpNo, Salary. If we join these files by EmpNo, the result
will be EmpNo, EmpName, and Salary.
29. What are the
mandatory keywords for join logical file?
JFILE –
Record level
JOIN –
Join level
JFLD –
Join level
JREF –
Join level
30. Explain
Self-Join with an example.
Join
a file to itself is known as self-join
Let PF01 has the fields of EmpNo,
EmpName, Salary, MGRID, Job.and has the following data
101 raja 43545 10001 engr
102 mohan 34544 10002 manager
103 kannan 43546 10002 clerk
10001 mani 54654 10002 MD
10002 ganesh 57656
Suppose the LF has EmpNo,
EmpName, and MGRName
101 raja mani
102 mohan ganesh
103 kannan ganesh
10001 mani ganesh
10002 ganesh xxxxxx
31. What is access
path and what are the various ways to creating access path?
It is a imaginary path, thro’
which the data of a file is accessed for processing. It tells the order in
which the record to be retrieved.
There are two types of access
path.
Key Sequenced access path.
In case of key sequenced access
path, the records accessed according with the key field.
Entry Sequenced access path
In case of Entry Sequenced access
path, the records accessed which the order they entered.
Here the record will be accessed
by either FIFO or LIFO or FCFO sequence, which is specified in the PF.
Select Omit criteria access path
32. Name three types of access
path maintenance?
There are three ways of building
or maintaining the access path.
Immediate
For every operation made on a
file, the access path, associated with it, is updated whether or not the path
is opened
Rebuild
Access path is maintained when
the file is open and various updates are recorded and the access path is
rebuilt every time when the access path is closed.
Delay
Access path is maintained when
file is opened and updates.
33. Why we need to maintain the access path?
Because more than one access path
is associated with one data, changing data in one file might cause changes to
be made in other files also.
34. Explain JDUPSEQ
and JDFTVAL.
JDUPSEQ
is used to specify the order in which records with duplicate join fields are
presented when the JLF is read.
JDFTVAL is used the system provides default
values for all fields, when a join to a secondary file does not produce any
records. If this keyword is not specified a record in the primary file for
which there is no corresponding record in secondary file is skipped.
35. Is it possible
to insert a record in a JLF?
No. It is
impossible to insert / update / delete record in a join logical file.
36. What keyword is used to join
several physical files into one logical file?
JFILE - Join
File
37. What are the
major differences between PF and LF?
|
Physical file
|
Logical file
|
|
It contains the actual data so it occupies memory space.
|
Can not occupy memory space
|
|
Single record format
|
Multiple record formats
|
|
Can be exist even with out LF
|
Can not exist with out PF
|
|
If you delete PF the LF also can be deleted.
|
If you delete a LF, the PF can not be deleted
|
|
The object type is PF
|
The object type is LF
|
|
CRTPF command is used to create such object
|
CRTLF command is used to create such type object
|
38. What is the difference
between a physical file and a logical file?
Physical files contain the data, a
logical file us an access path to the physical data
39. How many record
formats in a LF ad a PF can have?
PF – One only record format
LF – 32 record formats
40. Can you copy data from a physical file to a logical file?
No.
41. What keyword is used to
reference the same field in another file?
REF – Reference
42. What is a Field
Reference File?
It is also a
physical file, which doesn’t have any data. It has only field description and
other physical files can refer these definitions by using ref or reffld
keyword. Its type is *PF.
43. What are two methods of
creating a record that consists of fields from two or more files?
Join LF and
OPNQRYF.
44. What command can be used to
clear a physical file?
CLRPFM - Clear Physical File Member
45. What is the keyword VALUES used for?
To set records
from a PF based on field values in storage.
46. What is the keyword COMP
used for?
To set records
from a PF using a comparison between two field values.
47. What is the keyword RANGE used for?
To set records
from a PF based on a min/max value of a field.
48. How many record
formats in a PF, LF, DSPF and SFL?
PF => 1
LF => minimum 1, maximum 32
DSPF => 1024
SFL => 512
49. What is a display file?
A displayable
screen file.
50. What are the keyword levels used in Display file?
File
level
Record
level
Field
level
51. What is Menu?
Menu
is a list of short cut commands. We can create Menu thro, STRSDA tool.
52. Define Menu and
what is the command to create menu?
Menu is a set of
shortcut-commands, which is used to choosing program or commands to execute. In
the menu, the text and list of commands are stored in two different objects.
The MNUDDS keeps the text and the MNUCMD keeps the list of commands. We are
creating menu by using STRSDA command. The default menu name is MAIN. We can check the menu with help of GO command
[Syntax GO <menu name>]
53. In the DDS keyword WINDOW
(___), what belongs inside of the parentheses?
Either the
coordinates of the window or the name of the record format.
54. What is the difference
between CA and CF command keys?
CA means that
screen validity checking is bypassed and no screen data is passed to the
program. CF means that screen validity checking is performed and screen data is
passed to the program.
55. What is a printer file?
A print layout
for a report that can be used by any program.
56. Why would a DSPF program use
a DSPSIZ keyword?
To select the
screen display size used.
57. What is the INDARA keyword
used for?
To store all
program indicators into a useable array.
58. What is the purpose of the
OVERLAY keyword?
To allow
multiple screen records to display at one time.
59. How can a programmer control
how data on a screen will display?
By using the
DSPATR keyword.
60. How you create
a trigger?
Trigger is an event to be
performed either before or after any change on your database. By using ADDPFTRG
we can create a trigger. There are six triggers can be defined each physical
file. These are Before-Insert, Before-Update, Before-Delete, After-Insert,
After-Update and After-Delete. We can remove the trigger by using RMVPFTRG
command.
Suppose that, if we are going to
delete some records from primary file, assume that file has the referential
constraint to a secondary file. In such case, we have to use the trigger
[Delete-Before] for deleting the dependent record from secondary file.
The parameters to be given while
creating the trigger are 1. The timing (before/after) 2.The trigger event
(update etc) and 3. The PF name
61. What is a
Journal?
Journal is an object of type *JRN which will records the activities
of the physical file. The information recorded by the journal is stored in an
object *JRNRCV called Journal
Receiver.
62. Various steps
of creating a Journal.
Steps to
Start Journaling
Create a
Journal Receiver CRTJRNRCV
(name, library)
Create a Journal CRTJRN
(Journal
name, library, journal receiver name, journal receiver library)
Start Journaling of a physical
file STRJRNPF
(Journal name,
library, physical file(s) name, physical file(s) library, journal receiver name,
journal receiver library)
Backup the physical file SAVOBJ
Steps to
end a Journaling
End
journaling a PF ENDJRNPF
Delete a
Journal DLTJRN
Delete
the last Journal Receiver DLTJRNRCV
Save
Journal Receivers SAVOBJ
The
commands are to be used in case of failure
Display
journal entries DSPJRN
Apply
journal changes APYJRNCHG
Remove
journal changes RMVJRNCHG
Restore a
saved object RSTOBJ
63. Explain
Commitment Control.
It is the extension of
journaling.
An Integrated transaction
recovery function is known as commitment control. Let we are going to insert a
record in some files. If system fails before the commit operation, all the
database changes are rolled back to the previous commit operation. If the
system issues the commit operation, the records are freeing.
Steps
involving for a commitment control
§ First
you have to create a journal for the physical file, which you want to apply
commitment control.
§ You
have to give commit keyword in F-Spec keyword.
§
64. What is the
difference in multiple formats LF and join LF?
In both the case we pick up
fields from more than one PF, but the multiple format LF wont join the fields
and have more than one record format and join LF actually joins the fields and
can have only one record format.
65. How will you
define the fields in display screen?
+ To define
3 Input - numeric
6 Output - numeric
9 Both - numeric
I Input – character
O Output - character
B Both – character
66. How will you
move the fields in display screen?
(-) sign
in front end and rear end to mark the field.
(=) to
move the field after marked.
(==) to
copy fields after marked.
(<) shift
to left.
(>) shift
to right.
(?) to
get the field name and length.
67. How will you
get the system values in display screen?
*date for date.
*time for time.
68. What is the
keyword must be used with PROTECT keyword?
OVERLAY.