DMS overview

Access methods

Start

Commands

Data media

BS2000

The organization of data in files

File names

Access protection

Files can also be conventional input/output files from programs and load modules that represent executable programs.

Related data is collected in one named unit known as a file.

In the DMS every file is assigned a name in accordance with clearly defined rules so that they can be unambiguously distinguished from other files. Here are some of the most important details ...

For example, a file is comprised of several data records having similar content, thus forming a logical unit with specified organization parameters, much like a list of telephone numbers or a list of employees.

Characters permitted: Letters (at least one letter), Numbers (1, 2, 3, etc.) The following special characters/symbols: minus (-), at (@), hashtag (#), dollar ($), period/dot (.)

Limitations: The first character must never be a special character or symbol Blanks must never be used

Length of file names: 41 characters, maximum

Rules for naming files in the DMS

A slash replaces exactly one random character.

Using wildcards to select files

Wildcards can be used in commands that are employed to select a specified number of files. For example, if you want to display all of the files sharing a specific pattern, a wildcard may be used in the command.

Examples:

A dot at the end of the name means that at least one random character follows the dot.

An asterisk replaces a random (or blank) character sequence.

DEMO

PROJECT1

CHART

PROC

Examples: PROJECT1.SRC.COB.DEMO (fully qualified) PROJECT1.SRC.COB. (partially qualified)

EXAMPLE

COB

TEST

ASS

Test your knowledge

SRC

LAD

File names with a dot at the end are partially qualified file names. Users can take several of these partially qualified file names and form fully qualified file names. This enables users to set up folder-like structures when organizing files that are related to each other.

Partially qualified and fully qualified file names

File names can have any length.

Every name must contain at least one letter.

Test

Blanks must not be used.

File names in the DMS

True

Well? Can you tell which of the following statements is true or false?

False

A special character can be used as the first character in a file name.

PROJECT1.LAD.

Partially qualified

PROJECT1.SRC.ASS.

PROJECT1.SRC.COB.CHART

Which of the following file names are fully qualified, and which ones are partially qualified?

PROJECT1.PROC.DEMO

Fully qualified

The organization of files on data media

Files are saved to data media. BS2000 mainframe environments usually include disk storage systems like ETERNUS DX and tape storage systems such as the virtual ETERNUS CS8000 archive system.

ETERNUS CS

ETERNUS DX

The data media within the systems are identified by name in BS2000. These names – the VSN (Volume Serial Number) or the archive number – may be up to six characters in length.

Jedes Pubset enthält einen Benutzerkatalog. Er regelt, welche Benutzer auf einen Pubset zugreifen dürfen. Darin eingetragen sind zudem die Berechtigungen für jeden Benutzer.

Jedes Pubset enthält auch einen Dateikatalog. Jeder Katalogeintrag beschreibt Eigenschaften einer Datei und die Datenträger, auf der die Daten dieser Datei abgelegt sind.

Innerhalb von Disk Storage Systemen und Net-Storage, also Speicherbereichen auf NAS-Systemen, gibt es als gemeinschaftlich markierte Datenträger, so genannte Volumes.

Gemeinschaftliche Volumes werden zu Pubsets zusammengefasst. Jedem Pubset ist eine eigene Katalogkennung, die CATID, zugeordnet, die bis zu vier Zeichen lang sein kann. Beispiel hier: ein Pubset mit drei Volumes.

In dieser Maske wird der Cursor nun zum Paramter SPACE bewegt und anschließend nochmals die Return-Taste gedrückt …

Diese Maske bietet nun die Möglichkeit, das Kommando zu spezifizieren …

Zum Paramter SPACE öffnen sich die Optionen, die angepasst werden können. Der Cursor wird nun beim Paramter SPACE zu RELATIVE bewegt und nochmals die Return-Taste gedrückt.

Im Parameter FILE-NAME wird die Datei INFO angegeben …

Jetzt werden PRIMARY-ALLOCATION und SECONDARY-ALLOCATION angezeigt. Man bewegt den Cursor zu PRIMARY-ALLOCATION und drückt nochmals die Return-Taste.

Nun ist man in der Parameterstruktur des DVS an der richtigen Stelle, um für die Datei INFO den Speicherplatz zu vergrößern.

Für die Datei INFO werden in dieser Maske die entsprechenden Parameter angezeigt. Man bewegt den Cursor zum Parameter SUPPORT, dort zu PUBLIC-DISK() und drückt die Return-Taste

Schritt 1: Eingabe des Kommandos MODIFY-FILE-ATTRIBUTES

Schauen Sie sich am Beispiel des Kommandos MODIFY-FILE-ATTRIBUTES jetzt an, wie einfach man sich durch die Parameterstruktur des DVS hangeln kann. Das Ziel: Für die Datei INFO soll der Speicherplatz, also der Primary oder Secondary Allocator, vergrößert werden.

Working with files in the DMS

CREATE-FILE For making new files

SHOW-FILE-ATTRIBUTES For displaying file attributes

DELETE-FILE For deleting files

Examples with one click

SHOW-FILE For displaying file content

Commands support efficient file management. SDF is the command language in BS2000. SDF is easy to understand – commands are entered in accordance with English sentence structure (verb – object).

COPY-FILE For copying files

As described earlier, the data that is to be processed by programs in BS2000 is compiled in files. When a file is created, it is also assigned storage space. Two important operands are involved when creating or altering files: the Primary Allocator and the Secondary Allocator.

Example with one click

The Primary Allocator determines how much space is assigned to a file.

Secondary Allocation

Primary Allocation

The Secondary Allocator indicates how much space should be added when the primary allotted capacity is completely utilized.

Data processing in the DMS with access methods

Data records

File

Logical block

CLOSE

Users can also process the data from files by means of programs. The DMS provides program interfaces for this purpose that allow for read and write access to data. Data processing is generally performed in three phases.

Processing depends on the structure of the file. The types: SequentialIndexed sequentialDirect access (block-oriented)

PROCESS

OPEN

See details

When a file is being closed, the logical link between the file and the user's application is rescinded, and the file attributes in the catalog are updated.

When a file is being opened, the logical link between the file and the user's application is set up, and all of the information needed for file processing is collected and provided for use.

See illustration

From the user and DMS perspective, the files are comprised of logical blocks which themselves can originate from smaller units and records. A logical block consists of a multiple of 2 KB (2048 bytes) and can range in size up to 32 KB. A logical block can contain many data records with variable or fixed record lengths, whereby the maximum record length must not exceed the size of a logical block.

The data in the files is processed in the memory and not directly on the data media. The transfer of data between the memory and the data media is accomplished through the access methods and their action macros, such as those for reading and writing. There are two types of access methods: block-oriented and record-oriented.

The most important access methods with typical write and read action macros are:

Access method UPAM SAM ISAM

Details

In the record-oriented access method SAM (Sequential Access Method), the logical sequence of the data records is the same as the physical sequence of the data records on the data medium.

Acces type block-oriented record-oriented record-oriented

Action macros PAM READ, PAM WRITE GET, PUT GET, PUT

The block-oriented access method UPAM always transfers whole logical blocks and delivers these to the program for processing.

In the record-oriented access method ISAM (Index Sequential Access Method), the logical sequence is determined by an index according to which the data is stored in a separate management domain.

Overview

Access protection for files

When a file is opened, the protection attributes of the file are checked to see whether a user is permitted to open this file via reading or writing. Depending on the access method, a file can be opened and processed via writing by several users at the same time. In such cases, users must make special settings when opening the file so that the DMS can verify file compatibility.

Protection against unauthorized reading, writing/alteration and deletion of an existing file is ensured by limiting the access rights and access type by specifying a security time period, the use of passwords, etc. Access mechanisms vary in terms of the type and degree of detail used to define the access protection for files. Several protective mechanisms can be used to safeguard files. The strongest specified protective mechanism should be applied to prevent any conflicts.

Standard access control for the protection attributes ACCESS and USER-ACCESSSimple access control list (Basic Access Control List (BACL))Definition of access profiles by means of GUARD (GUARDS is a functionality in the SECOS software product)Stipulation of passwords (read, write and execute)Protection time frames within which a file may not be alteredEncrypted file storage

The DMS offers the following mechanisms to protect files:

Access rights

Encrypted file storage

Access rights (GUARDS)

Protection via time frames

Standard access control (ACCESS/USER-ACCESS)

Simple access control list (BACL)

Protection via password

Each pubset also contains a file catalog. Each catalog entry describes the file attributes and the data media which carry the data for the file.

Each pubset contains a user catalog. The user catalog determines which users are allowed to access a pubset. It contains the authorizations for every user.

According to the principle shown in the diagram, the data is stored on the data media in accordance with unambiguous path names in the DMS. A path name is comprised of a storage location, user ID and the file name.

These shared volumes are gathered together in pubsets. Every pubset is assigned its own catalog identification (CATID), which can be up to four characters long. This example shows a pubset with three volumes.

The disk storage systems and net storage, which are the areas designated for storage in NAS systems, also include so-called volumes, which are data media marked for shared usage.

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Organisation von Daten in Dateien

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Using the command MODIFY-FILE-ATTRIBUTES as an example, see how the operand structure of the DMS functions (alternatively, commands can be entered directly in the line). The objective: The storage space for the INFO file, in other words the Primary or Secondary Allocator, is to be expanded.

The sub-screen of the SUPPORT operand then opens for the INFO file. The user overwrites *UNCHANGED with *PUBLIC-Disk(? and then presses the return key.

Step 1: Enter the command /MODIFY-FILE-ATTRIBUTES?

On this screen the user moves the cursor to the SPACE operand and enters a question mark (?). The sub-screen of SPACE then opens. The user overwrites *UNCHANGED with *RELATIVE(? and again presses the return key.

The user now has the option of specifying the command on the screen. After entering the INFO file name, we move the cursor to the support operand and enter a question mark (?) there.

If the user now enters a question mark (?) for PRIMARY-ALLOCATION and SECONDARY-ALLOCATION, the help screen will appear. Instead of entering a question mark (?), the user can enter a value directly after the operands – in this case, so doing would increase the storage space assigned to the INFO file.